Saving One of North America's Rarest Shrubs

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The chance to save a species from certain extinction cannot be wasted. When the opportunity presents itself, I believe it is our duty to do so. Back in 2010, such an opportunity presented itself to the state of California and what follows is a heroic demonstration of the lengths dedicated individuals will go to protect biodiversity. Thought to be extinct for 60 years, the Franciscan manzanita (Arctostaphylos franciscana) has been given a second chance at life on this planet.

California is known the world over for its staggering biodiversity. Thanks to a multitude of factors that include wide variations in soil and climate types, California boasts an amazing variety of plant life. Some of the most Californian of these plants belong to a group of shrubs and trees collectively referred to as 'manzanitas.' These plants are members of the genus Arctostaphylos, which hails from the family Ericaceae, and sport wonderful red bark, small green leaves, and lovely bell-shaped flowers. Of the approximately 105 species, subspecies, and varieties of manzanita known to science, 95 of them can be found growing in California.

It has been suggested that manzanitas as a whole are a relatively recent taxon, having arisen sometime during the Middle Miocene. This fact complicates their taxonomy a bit because such a rapid radiation has led manzanita authorities to recognize a multitude of subspecies and varieties. In California, there are also many endemic species that owe their existence in part to the state's complicated geologic history. Some of these manzanitas are exceedingly rare, having only been found growing in one or a few locations. Sadly, untold species were probably lost as California was settled and human development cleared the land. 

Such was the case for the Franciscan manzanita. Its discovery dates back to the late 1800's. California botanist and manzanita expert, Alice Eastwood, originally collected this plant on serpentine soils around the San Francisco Bay Area. In the years following, the growing human population began putting lots of pressure on the surrounding landscape.

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Botanists like Eastwood recognized this and went to work doing what they could to save specimens from the onslaught of bulldozers. Luckily, the Franciscan manzanita was one such species. A few individuals were dug up, rooted, and their progeny were distributed to various botanical gardens. By the 1940's, the last known wild population of Franciscan manzanita were torn up and replaced by the unending tide of human expansion into the Bay Area.

It was apparent that the Franciscan manzanita was gone for good. Nothing was left of its original populations outside of botanical gardens. It was officially declared extinct in the wild. Decades went by without much thought for this plant outside of a few botanical circles. All of that changed in 2009.

It was in 2009 when a project began to replace a stretch of roadway called Doyle Drive. It was a massive project and a lot of effort was invested to remove the resident vegetation from the site before work could start in earnest. Native vegetation was salvaged to be used in restoration projects but most of the clearing involved the removal of aggressive roadside trees. A chipper was brought in to turn the trees into wood chips. Thanks to a bit of serendipity, a single area of vegetation bounded on all sides by busy highway was spared from wood chip piles. Apparently the only reason for this was because a patrol car had been parked there during the chipping operation.

Cleared of tall, weedy trees, this small island of vegetation had become visible by road for the first time in decades. That fall, a botanist by the name of Daniel Gluesenkamp was driving by the construction site when he noticed an odd looking shrub growing there. Luckily, he knew enough about manzanitas to know something was different about this shrub. Returning to the site with fellow botanists, Gluesenkamp and others confirmed that this odd shrubby manzanita was in fact the sole surviving wild Franciscan manzanita. Needless to say, this caused a bit of a stir among conservationists.

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The shrub had obviously been growing in that little island of serpentine soils for quite some time. The surrounding vegetation had effectively concealed its presence from the hustle and bustle of commuters that crisscross this section of on and off ramps every day. Oddly enough, this single plant likely owes its entire existence to the disturbance that created the highway in the first place. Manzanitas lay down a persistent seed bank year after year and those seeds can remain dormant until disturbance, usually fire but in this case road construction, awakens them from their slumber. It is likely that road crews had originally disturbed the serpentine soils just enough that this single Franciscan manzanita was able to germinate and survive.

The rediscovery of the last wild Franciscan manzanita was bitter sweet. On the one hand, a species thought extinct for 60 years had been rediscovered. On the other hand, this single individual was extremely stressed by years of noxious car exhaust and now, the sudden influx of sunlight due to the removal of the trees that once sheltered it. What's more, this small island of vegetation was doomed to destruction due to current highway construction. It quickly became apparent that if this plant had any chance of survival, something drastic had to be done.

Many possible rescue scenarios were considered, from cloning the plant to moving bits of it into botanical gardens. In the end, the most heroic option was decided on - this single Franciscan manzanita was going to be relocated to a managed natural area with a similar soil composition and microclimate.

Moving an established shrub is not easy, especially when that particular individual is already stressed to the max. As such, numerous safeguards were enacted to preserve the genetic legacy of this remaining wild individual just in case it did not survive the ordeal. Stem cuttings were taken so that they could be rooted and cloned in a lab. Rooted branches were cut and taken to greenhouses to be grown up to self-sustaining individuals. Numerous seeds were collected from the surprising amount of ripe fruits present on the shrub that year. Finally, soil containing years of this Franciscan manzanita's seedbank as well as the microbial community associated with the roots, were collected and stored to help in future reintroduction efforts.

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Finally, the day came when the plant was to be dug up and moved. Trenches were dug around the root mass and a dozen metal pipes were driven into the soil 2 feet below the plant so that the shrub could safely be separated from the soil in which it had been growing all its life. These pipes were then bolted to I-beams and a crane was used to hoist the manzanita up and out of the precarious spot that nurtured it in secret for all those years.

Upon arriving at its new home, experts left nothing to chance. The shrub was monitored daily for the first ten days of its arrival followed by continued weekly visits after that. As anyone that gardens knows, new plantings must be babied a bit before they become established.  For over a year, this single shrub was sheltered from direct sun, pruned of any dead and sickly branches, and carefully weeded to minimize competition. Amazingly, thanks to the coordinated effort of conservationists, the state of California, and road crews, this single individual lives on in the wild.

Of course, one single individual is not enough to save this species from extinction. At current, cuttings, and seeds provide a great starting place for further reintroduction efforts. Similarly, and most importantly, a bit of foresight on the part of a handful of dedicated botanists nearly a century ago means that the presence of several unique genetic lines of this species living in botanical gardens means that at least some genetic variability can be introduced into the restoration efforts of the Franciscan manzanita.

In an ideal world, conservation would never have to start with a single remaining individual. As we all know, however, this is not an ideal world. Still, this story provides us with inspiration and a sense of hope that if we can work together, amazing things can be done to preserve and restore at least some of what has been lost. The Franciscan manzanita is but one species that desperately needs our help an attention. It is a poignant reminder to never give up and to keep working hard on protecting and restoring biodiversity.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4]

 

The Mystery of the Ghost Plant

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As houseplants enjoy a resurgence in our culture, untold numbers of novice and expert growers alike will have undoubtedly tried their luck at a succulent or two. Succulent, of course, is not a taxonomic division, but rather a way of describing the anatomy of myriad plants adapted to harsh, dry environments around the world. One of the most common succulents in the trade is the ghost plant (Graptopetalum paraguayense).

I would bet that, if you are reading this and you grow houseplants, you have probably grown a ghost plant at one point or another. They are easy to grow and will propagate a whole new plant from only a single leaf. Despite its worldwide popularity, the ghost plant is shrouded in mystery and confusion. To date, we know next to nothing about its ecology. Much of this stems from poor record keeping and the fact that we have no idea exactly where this species originated.

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That's right, we do not know the location of its native habitat. Records indicate that the first plants to find their way into human hands were imported into New York in 1904. Apparently, they were growing as "weeds" at the base of some South American cacti. Plants were lucky enough to wind up in the hands of competent botanists and the species has ended up with the name Graptopetalum paraguayense. The specific epithet "paraguayense" was an indication of much confusion to come as it was thought that the ghost plant originated in Paraguay.

Time has barely improved our knowledge. Considering many of its relatives hail from Mexico, it gradually became more apparent that South America could not claim this species as its own. Luck changed only relatively recently with the discovery of a population of a unique color variant of the ghost plant on a single mountain in northeastern Mexico. A thorough search of the area did not reveal any plants that resemble the plant so many of us know and love. It has been suggested that the original population from which the type species was described is probably growing atop an isolated mountain peak somewhere nearby in the Chihuahuan Desert.

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Despite all of the mystery surrounding this species, we can nonetheless elucidate some aspects about its biology by observing plants in cultivation. It goes without saying that the ghost plant is a species of dry, nutrient-poor habitats. Its succulence and tolerance of a wide array of soil conditions is a testament to its hardy disposition. Also, if plants are grown in full sun, they develop a bluish, waxy coating on their leaves. This is likely a form of sunscreen that the plant produces to protect it from sun scorch. As such, one can assume that its native habitat is quite sunny, though its ability to tolerate shade suggests it likely shares its habitat with shrubby vegetation as well. Given enough time and proper care, ghost plants will produce sprays of erect, 5 pointed flowers. It is not known who might pollinate them in the wild.

It is always interesting to me that a plant can be so well known to growers while at the same time being a complete mystery in every other way. A search of the literature shows that most of the scientific attention given to the ghost plant centers on potentially useful compounds that can be extracted from its tissues. Such is the case for far too many plant species, both known and unknown alike. Perhaps, in the not too distant future, some intrepid botanist will at last scramble up the right mountain and rediscover the original habitat of this wonderful plant. Until then, I hope this small introduction provides you with a new found appreciation for this wonderfully adaptable houseplant.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

 

Leafy Cacti?

  Pereskia aculeata

Pereskia aculeata

At first glance, there is little about a Pereskia that would suggest a relation to what we know as cacti. Even a second, third, and forth glance probably wouldn't do much to persuade the casual observer that these plants have a place on cacti family tree. All preconceptions aside, Pereskia are in fact members of the family Cactaceae and quite interesting ones at that.

Most people readily recognize the leafless, spiny green stems of a cactus. Indeed, this would appear to be a unifying character of the family. Pereskia is proof that this is not the case. Though other cacti occasionally produce either tiny, vestigial leaves or stubby succulent leaves, Pereskia really break the mold by producing broad, flattened leaves with only a hint of succulence.

 Pereskia spines are produced from areoles in typical cactus fashion.

Pereskia spines are produced from areoles in typical cactus fashion.

What's more, instead of clusters of Opuntia-like pads or large, columnar trunks, Pereskia are mainly shrubby plants with a handful of scrambling climbers mixed in. Similar to their more succulent cousins, the trunks of Pereskia are usually adorned with clusters of long spines for protection. Additionally, each species produces the large, showy, cup-like blooms we have come to expect from cacti.

They are certainly as odd as they are beautiful. As it stands right now, taxonomists recognize two clades of Pereskia - Clade A, which are native to a region comprising the Gulf of Mexico and Caribbean Sea (this group is currently listed under the name Leuenbergeria) and Clade B, which are native to regions just south of the Amazon Basin. This may seem superficial to most of us but the distinction between these groups has a lot to teach us about the evolution of what we know of as cacti. 

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Pereskia grandifolia

Genetically speaking, the genus Pereskia sorts out at the base of the cactus family tree. Pereskia are in fact sister to all other cacti. This is where the distinction between the two Pereskia clades gets interesting. Clade A appears to be the older of the two and all members of this group form bark early on in their development and their stems lack a feature present in all other cacti - stomata. Stomata are microscopic pours that allow the exchange of gases like CO2 and oxygen. Clabe B, on the other hand, delay bark formation until later in life and all of them produce stomata on their stems.

The reason this distinction is important is because all other cacti produce stomata on their stems as well. As such, their base at the bottom of the cactus tree not only shows us what the ancestral from of cactus must have looked like, it also paints a relatively detailed picture of the evolutionary trajectory of subsequent cacti lineages. It would appear that the ancestor of all cacti started out as leafy shrubs that lacked the ability to perform stem photosynthesis. Subsequent evolution saw a delay in bark formation, the presence of stomata on the stem, and the start of stem photosynthesis, which is a defining feature of all other cacti.

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Pereskia aculeata

If you are as excited about Pereskia as I am, then you , my friend, are in luck. A handful of Pereskia species have found their way into the horticulture trade. With a little luck attention to detail, you too can share you home with one of these wonderful plants. Just be warned, they get tall and their spines, which are often hidden by the leaves, are a force to be reckoned with. Tread lightly with these wonderfully odd cacti. Celebrate their as the evolutionary wonders that they are!

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]

 

 

Of Bluebells and Fungi

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Whether in your garden or in the woods, common bluebells (Hyacinthoides non-scripta) are a delightful respite from the dreary months of winter. It should come as no surprise that these spring geophytes are a staple in temperate gardens the world over. And, as amazing as they are in the garden, bluebells are downright fascinating in the wild.

Bluebells can be found growing naturally from the northwestern corner of Spain north into the British Isles. They are largely a woodland species, though finding them in meadows isn't uncommon. They are especially common in sites that have not experienced much soil disturbance. In fact, large bluebell populations are used as indicators of ancient wood lots.

Being geophytes, bluebells cram growth and reproduction into a few short weeks in spring. We tend to think of plants like this as denizens of shade, however, most geophytes get going long before the canopy trees have leafed out. As such, these plants are more accurately sun bathers. On warm days, various bees can be seen visiting the pendulous flowers, with the champion pollinator being the humble bumble bees.

The above ground beauty of bluebells tends to distract us from learning much about their ecology. That hasn't stopped determined scientists though. Plenty of work has been done looking at how bluebells make their living and get on with their botanical neighbors. In fact, research is turning up some incredible data regarding bluebells and mycorrhizal fungi.

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Bluebell seeds tend not to travel very far, most often germinating near the base of the parent. Germination occurs in the fall when temperatures begin to drop and the rains pick up. Interestingly, bluebell seeds actually germinate within the leaf litter and begin putting down their initial root before the first frosts. Often this root is contractile, pulling the tiny seedling down into the soil where it is less likely to freeze. During their first year, phosphorus levels are high. Not only does the nutrient-rich endosperm supply the seedling with much of its initial needs, abundant phosphorus near the soil surface supplies more than enough for young plants. This changes as the plants age and change their position within the soil.

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Over the next 4 to 5 years, the bluebell's contractile roots pull it deeper down into the soil, taking it out of the reach of predators and frost. This also takes them farther away from the nutrient-rich surface layers. What's more, the roots of older bluebells are rather simple structures. They do not branch much, if at all, and they certainly do not have enough surface area for proper nutrient uptake. This is where mycorrhizae come in.

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Bluebells partner with a group of fungi called arbuscular mycorrhiza, which penetrate the root cells, thus greatly expanding the effective rooting zone of the plant. Plants pay these fungi in carbohydrates produced during photosynthesis and in return, the fungi provide the plants with access to far more nutrients than they would be able to get without them. One of the main nutrients plants gain from these symbiotic fungi is phosphorus.

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For bluebells, with age comes new habitat, and with new habitat comes an increased need for nutrients. This is why bluebells become more dependent on arbuscular mycorrhiza as they age. In fact, plants grown without these fungi do not come close to breaking even on the nutrients needed for growth and maintenance and thus live a shortened life of diminishing returns. This is an opposite pattern from what we tend to expect out of mycorrhizal-dependent plants. Normally its the seedlings that cannot live without mycorrhizal symbionts. It just goes to show you that even familiar species like the bluebell can offer us novel insights into the myriad ways in which plants eke out a living.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2]

 

One Mustard, Many Flavors

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What do kale, broccoli, cauliflower, Brussel sprouts, and cabbage have in common? They are all different cultivars of the same species!

Wild cabbage (Brassica oleracea) is native to coastal parts of southern and western Europe. In its native habitat, wild cabbage is very tolerant of salty, limey soils but not so tolerant of competition. Because of this, it tends to grow mainly on limestone sea cliffs where few other plants can dig their roots in.

Despite their popularity as delicious, healthy vegetables, as well as their long history of cultivation, there is scant record of this plant before Greek and Roman times. Some feel that this is one of the oldest plants in cultivation. Along with the countless number of edible cultivars, the wild form of Brassica oleracea can be found growing throughout the world, no doubt thanks to its popularity among humans.

I am always amazed by how little we know about crop wild relatives. Despite the popularity of its many agricultural cultivars, relatively little attention has been paid to B. oleracea in the wild. What we do know is that at least two subspecies have been identified - B. oleracea ssp. bourgeaui and B. oleracea L. ssp. oleracea. As far as anyone can tell, subspecies 'oleracea' is the most wide spread in its distribution whereas subspecies 'bourgeaui'  is only known from the Canary Islands. 

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B. oleracea's long history with humans confuses matters quite a bit. Because it has been cultivated for thousands of years, identifying which populations represent wild individuals and which represent ancient introductions is exceedingly difficult. Such investigations are made all the more difficult by a lack of funding for the kind of research that would be needed to elucidate some of these mysteries. We know so little about wild B. oleracea that the IUCN considers is a species to be "data deficient."

It seems to appreciate cool, moist areas and will sometimes escape from cultivation if conditions are right, thus leading to the confusion mentioned above. It is amazing to look at this plant and ponder all the ways in which humans have selectively bred it into the myriad shapes, sizes, and flavors we know and love (or hate) today! However, we must pay more attention to the wild progenitors of our favorite crops. They harbor much needed genetic diversity as well as clues to how these plants are going to fare as our climates continue to change.

Photo Credit: [1] [2]

Further Reading: [1] [2] [3]

Trout Lily Appreciation

This video is a celebration of the white trout lily (Erythronium albidum) and its various spring ephemeral neighbors. We even talk about the threat that invasive species like garlic mustard (Alliara petiolata).

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Botanist
Track:
https://verdant-realm-botanist.bandcamp.com/

Prescribed Fire On An Illinois Prairie

Prairies are fire adapted ecosystems. For far too long, fires were sequestered. Today, more and more communities are coming around to the fact that fire can be used as a tool to bring life back to these endangered ecosystems. In this video, we get hands on experience with fire as a prairie restoration tool.

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Stranger In My Town
Track: Terra
https://strangerinmytown.bandcamp.com/

 

Early Spring Ephemerals

Join us as we go in search of some of the earliest spring ephemerals. In this episode we come face to face with the aptly named harbinger of spring (Erigenia bulbosa) and the lovely Hepatica nobilis.

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Stranger In My Town
Track: Air
https://strangerinmytown.bandcamp.com/

Life On a Floodplain

Floodplains can be pretty rough places for plant life. Despite readily a available water supply, the unpredictable, disturbance-prone nature of these habitats means that static lifeforms such as plants need to be quite adaptable to survive and persist. Join In Defense of Plants for a brief look at this sort of ecosystem.

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Somali Yacht Club
Track: Up In The Sky
http://somaliyachtclub.bandcamp.com

The Intriguing Pollination of a Central American Anthurium

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As an avid gardener of both indoors and out, there are few better experiences than getting to see familiar plants growing in the wild for the first time. That experience is made all the better when you find out new and interesting facts about their ecology. On a recent trip to Costa Rica, I was introduced to a wide variety of Anthurium species. I marveled at how amazing these plants look in situ and was taken aback to learn that many produce flowers with intoxicating aromas.

I was also extremely fortunate to be in the presence of some aroid experts during this trip and their knowledge fueled my interest in getting up close and personal with what little time I had with these plants. They were able to ID the plants and introduce me to their biology. One species in particular has been the subject of interest in an ongoing pollination study that has proven to be unique.

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The plant in question is known scientifically as Anthurium acutifolium and it is rather charming once you get to know it. It is a terrestrial plant with relatively large leaves for its overall size. Its range includes portions of lowland Costa Rica and Panama. Its flowers are typical of what one would expect out of this family. They are fused into a type of inflorescence known as a spadix and can range in color from white to green and occasionally red. If you are lucky to visit the spadix between roughly 8:00 AM and 12:30 PM, you may notice a rich scent that, to me, is impossible to describe in words.

It's this scent that sets the stage for pollination in this species. During some down time, University of Vienna grad student Florian Etl discovered that the spadix of A. acutifolium was getting a lot of attention from a particular species of small bee. Closer inspection revealed that they were all males of a species of oil-collecting bee known as Paratetrapedia chocoensis. Now, the females of these oil collecting bees are well known in the pollination literature. They visit flowers that secrete special oils that the females then use to build nests and feed their young. This is why the attention from male bees was so intriguing.

 A: A male  P. chocoensis  bee approaching a scented spadix of an inflorescence of  A. acutifolium . B: The abdominal mopping behavior of male  P. chocoensis  oil bees on a spadix. C: Ventral side of the abdomen of a male  P.chocoensis  covered with pollen. D: A male  P. chocoensis  bee on a spadix of an inflorescence of  A. acutifolium , touching the pollen shedding anthers. E: Pubescent region pressed on the surface of  A. acutifolium  during the mopping behavior. F: A scented inflorescence of  A. acutifolium  with three male  P. chocoensis  individuals. G: Image of the abdomen of a male  P.chocensis  in lateral view showing the conspicuous pubescent region. ( SOURCE )

A: A male P. chocoensis bee approaching a scented spadix of an inflorescence of A. acutifolium. B: The abdominal mopping behavior of male P. chocoensis oil bees on a spadix. C: Ventral side of the abdomen of a male P.chocoensis covered with pollen. D: A male P. chocoensis bee on a spadix of an inflorescence of A. acutifolium, touching the pollen shedding anthers. E: Pubescent region pressed on the surface of A. acutifolium during the mopping behavior. F: A scented inflorescence of A. acutifolium with three male P. chocoensis individuals. G: Image of the abdomen of a male P.chocensis in lateral view showing the conspicuous pubescent region. (SOURCE)

Males would land on the spadix and begin rubbing the bottom of their abdomen along its surface. In doing so, they inevitably picked up and deposited pollen. To date, such behavior was unknown among male oil bees. What exactly were these male bees up to?

As it turns out, the males were collecting fragrances. Close inspection of their morphology revealed that each male has a small patch of dense hairs underneath their abdomen. The males are definitely not after fatty oils or nectar as A. acutifolium does not secrete either of these substances. Instead, it would appear that the male oil bees are there to collect scent, which is mopped up by that dense patch of hairs. Even more remarkable is the fact that in order to properly collect these fragrance compounds, the bees are likely using solvents that they have collected from other flowering plant species around the forest.

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What they are doing with these scent compounds remains a mystery but some potential clues lie in another scent/pollination system. Male orchid bees perform similar scent-collecting activities in order to procure unique scent bouquets. Though the exact function of their scent collecting is not known either, we do know that these scents are used in the process of finding and procuring mates. It is likely that these male oil bees are using them in a similar way.

Taken together, these data suggest that a very specific pollination syndrome involving A. acutifolium and male oil bees has evolved in Central American forests. No other insects were observed visiting the flowers of A. acutifolium and the scents only ever attracted males of these specific oil bees during the hours in which the spadix was actively producing the compounds. This is a remarkable pollination syndrome and one that encourages us to start looking elsewhere in the forest. This, my friends, is why there is no substitute for simply taking the time to observe nature. We must take the time to get outside and poke around because we stand to miss out on so much of what makes our world tick and without such knowledge, we risk losing so much. 

Photo Credits: Florian Etl [1]

Further Reading: [1]

The Desert Mistletoe: Evolution In Action

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There are a multitude of mistletoes on this planet (for example: 1, 2, 3) and all of them are parasites to one degree or another. I find parasitic plants absolutely fascinating as there are many variations on this lifestyle as there are hosts to parasitize. On a recent botanical adventure in the Sonoran Desert, I met yet another representative of this group - the desert mistletoe (Phoradendron californicum). Once I knew what I was looking at, I could not wait to do some research. As it turns out, this species has garnered quite a bit of attention over the years and it is teaching us some interesting tidbits on how parasites may evolve.

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The desert mistletoe is not hard to spot, especially during the driest parts of the year when most of its host trees have shed their leaves. It looks like a leafless tangled mass of pendulous stems sitting among the branches of larger shrubs and trees. It can be found growing throughout both the Mojave and Sonoran deserts and appears to prefer leguminous trees including palo verde (Parkinsonia florida), mesquite (Prosopis spp.), and Acacia.

The desert mistletoe is a type of hemiparasite, which means it is capable of performing photosynthesis but nonetheless relies on its host tree for water and other nutrients. Lacking leaves, the desert mistletoe meets all of its photosynthetic needs via its green stems. Its leafless habit also makes its flowers and fruit all the more conspicuous. Despite their small size, its flowers are really worth closer inspection. When in bloom, a desert mistletoe comes alive with the hum of various insects looking for energy-rich nectar and pollen. Even before you spot them, you can easily tell if there is a blooming mistletoe nearby as the flowers give off a wonderfully sweet aroma. It appears that the desert mistletoe takes no chances when it comes to reproduction in such an arid climate.

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As I mentioned above, the desert mistletoe has been the subject of inquiry over the last few decades. Researchers interested in how parasitic plants evolve have illuminated some intriguing aspects of the biology of this species, especially as its relates to host preference. It would appear that our interest in this species seems to be situated at an important time in its evolutionary history. Not all populations of desert mistletoe "behave" in the same way. In fact, each seems to be heading towards more intense specialization based on its preferred host.

By performing seed transplant experiments, researchers have demonstrated that various populations of desert mistletoe seem to be specializing on specific tree species. For instance, when seeds collected from mistletoe growing on Acacia were placed on paleo verde or mesquite, they experienced significantly less germination than if they were placed on another Acacia. Though the exact mechanisms aren't clear at this point in time, evidence suggests that the success of desert mistletoe may be influenced by various hormone levels within the host tree, with isolated populations becoming more specialized on the chemistry of their specific host in that region.

Speaking of isolation, there is also evidence to show that populations of desert mistletoe growing on different host trees are reproductively isolated as well. Populations growing on mesquite trees flower significantly later than populations growing on Acacia or palo verde. Essentially this means that their genes never have the chance to mix, thus increasing the differences between these populations. Again, it is not entirely certain how the host tree may be influencing mistletoe flowering time, however, hormones and water availability are thought to play a role.

Another intriguing idea, and one that has yet to be tested, are the roles that seed dispersers may play out in this evolutionary drama. After pollination, the desert mistletoe produces copious amounts of bright red berries that birds find irresistible. Two birds in particular, the northern mockingbird and the Phainopepla, aggressively defend fruiting mistletoe shrubs within their territories. It could be possible that these birds may be influencing which trees the seeds of the desert mistletoe end up on. Again, this is just a hypothesis but one that certainly deserves more attention.

 A Phainopepla on the lookout for mistletoe berries.

A Phainopepla on the lookout for mistletoe berries.

Love them or hate them, there is something worth admiring about mistletoes. At the very least, they are important components of their native ecology. What's more, species like the desert mistletoe have a lot to teach us about the way in which species interact and what that means for biodiversity.

Photo Credit: [1]

Further Reading: [1] [2] [3] [4]

North America's Pachysandra

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In the interest of full disclosure, I have never been a fan of garden variety Pachysandra. Long before I had any interest in plants or gardening, there was something about this groundcover that simply did not appeal to me. Fast forward more than a decade and my views on the use of Asian Pachysandra in the garden have not changed much. You can imagine my surprise then when I learned that North America has its own representative of this genus - the Allegheny spurge (Pachysandra procumbens).

My introduction to P. procumbens happened during a tour of the Highlands Botanical Garden in Highlands, North Carolina. I recognized its shape and my initial reaction was alarm that a garden specializing in native plants would showcase a non-native species. My worry was quickly put to rest as the sign informed me that this lovely groundcover was in fact indigenous to this region. Indeed, P. procumbens can be found growing in shady forest soils from North Carolina down to Florida and Texas.

This species is yet another representative of a curious disjunction in major plant lineages between North America and eastern Asia. Whereas North America has this single species of Pachysandra, eastern Asia boasts two, P. axillaris and P. terminalis. Such a large gap in the distribution of this genus (as well as many others) seems a bit strange until one considered the biogeographic history of the two continents.

Many thousands of years ago, sea levels were much lower than they are today. This exposed land bridges between continents which today are hundreds of feet under water. During favorable climatic periods, Asia and North America likely shared a considerable amount of their respective floras, a fact we still find evidence of today. The Pachysandra are but one example of a once connected distribution that has been fragmented by subsequent sea level rise. Fossil records of Pachysandra have been found in regions of British Columbia, Washington, Oregon, Wyoming, and North and South Dakota and provide further confirmation of this.

As a species, P. procumbens is considered a subshrub. It is slow growing but given time, populations can grow to impressive sizes. In spring, numerous fragrant, white flower spikes emerge that are slowly eclipsed by the flush of spring leaf growth. The flowers themselves are intriguing structures worthy of close inspection. Their robust form is what gives this genus its name. "Pachys" is Greek for thick and "andros" is Greek for male, which refers to the thickened filaments that support the anthers.

It is hard to say for sure why this species is not as popular in horticulture as its Asian cousins. It tolerates a wide variety of soil types and does well in shade. What's more, it is mostly ignored by all but the hungriest of deer. And, at the end of the day, it took this species to change my mind about Pachysandra. After all, each and every species has a story to tell.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

Daffodil Insights

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Daffodils seem to be everywhere. Their horticultural popularity means that, for many of us, these plants are among the first flowers we see each spring. Daffodils are so commonplace that it's as if they evolved to live in our gardens and nowhere else. Indeed, daffodils have had a long, long history with human civilization, so much so that it is hard to say when our species first started to cohabitate. Our familiarity with these plants belies an intriguing natural history. What follows is a brief overview of the world of daffodils. 

If you are like me, then you may have gone through most of your life not noticing much difference between garden variety daffodils. Though many of us will be familiar with only a handful of daffodil species and cultivars, these introductions barely scratch the surface. One may be surprised to learn that as of 2008, more than 28,000 daffodil varieties have been named and that number continues to grow each and every year. Even outside of the garden, there is some serious debate over the number of daffodil species, much of this having to do with what constitutes a species in this group.

  Narcissus poeticus

Narcissus poeticus

As I write this, all daffodils fall under the genus Narcissus. Estimates as to the number of species within Narcissus range from as few as 50 to as many as 80. The genus itself sits within the family Amaryllidaceae and is believed to have originated somewhere between the late Oligocene and early Miocene, some 18 to 30 million years ago. Despite its current global distribution, Narcissus are largely Mediterranean plants, with peak diversity occurring on the Iberian Peninsula. However, thanks to the aforementioned long and complicated history in cultivation, it has become quite difficult to understand the full range of diversity in form and habitat of many species. To understand this, we first need to understand a bit about their reproductive habits.

Much of the evolution of Narcissus seems to center around floral morphology and geographic isolation. More specifically, the length of the floral tube or "corona" and the position of the sexual organs within, dictates just who can effectively pollinate these plants. The corona itself is not made up of petals or sepals but instead, its tube-like appearance is due to a fusion of the stamens into the famous trumpet-like tube we know and love.

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Variation in corona shape and size has led to the evolution of three major pollination strategies within this genus. The first form is the daffodil form, whose stigma is situated at the mouth of the corolla, well beyond the 6 anthers. This form is largely pollinated by larger bees. The second form is the paperwhite form, whose stigma is situated more closely to or completely below the anthers at the mouth of the corona. This form is largely pollinated by various Lepidoptera as well as long tongued bees and flies. The third form is the triandrus form, which exhibits three distinct variations on stigma and anther length, all of which are situated deep within the long, narrow corona. The pendant presentation of the flowers in this group is thought to restrict various butterflies and moths from entering the flower in favor of bees.

  Narcissus tazetta

Narcissus tazetta

The variations on these themes has led to much reproductive isolation among various Narcissus populations. Plants that enable one type of pollinator usually do so at the exclusion of others. Reproductive isolation plus geographic isolation brought on by differences in soil types, habitat types, and altitudinal preferences is thought to have led to a rapid radiation of these plants across the Mediterranean. All of this has gotten extremely complicated ever since humans first took a fancy to these bulbs.

  Narcissus cyclamineus

Narcissus cyclamineus

Reproductive isolation is not perfect in these plants and natural hybrid zones do exist where the ranges of two species overlap. However, hybridization is made much easier with the helping hand of humans. Whether via landscape disturbance or direct intervention, human activity has caused an uptick in Narcissus hybridization. For centuries, we have been mixing these plants and moving them around with little to no record as to where they originated. What's more, populations frequently thought of as native are actually nothing more than naturalized individuals from ancient, long-forgotten introductions. For instance, Narcissus populations in places like China, Japan, and even Great Britain originated in this manner.

All of this mixing, matching, and hybridizing lends to some serious difficulty in delineating species boundaries. It would totally be within the bounds of reason to ask if some of the what we think of as species represent true species or simply geographic varieties on the path to further speciation. This, however, is largely speculative and will require much deeper dives into Narcissus phylogenetics.

  Narcissus triandrus

Narcissus triandrus

Despite all of the confusion surrounding accurate Narcissus taxonomy, there are in fact plenty of true species worth getting to know. These range in form and habit far more than one would expect from horticulture. There are large Narcissus, small Narcissus, there are Narcissus with yellow flowers and Narcissus with white flowers, some with upright flowers and some with pendant flowers. There are even a handful of fall blooming Narcissus. The variety of this genus is staggering if you are not prepared for it.

  Narcissus viridiflorus  - a green, fall-blooming daffodil

Narcissus viridiflorus - a green, fall-blooming daffodil

After pollination, the various Narcissus employ a seed dispersal strategy that doesn't get talked about enough in reference to this group. Attached to each hard, black seed are fatty structures known as eliasomes. Eliasomes attract ants. Like many spring flowering plant species around the globe, Narcissus utilize ants as seed dispersers. Ants pick up the seeds and bring them back to their nests. They go about removing the eliasomes and then discard the seed. The seed, safely tucked away in a nutrient-rich ant midden, has a much higher chance of germination and survival than if things were left up to simple chance. It remains to be seen whether or not Narcissus obtain similar seed dispersal benefits from ants outside of their native range. Certainly Narcissus populations persist and naturalize readily, however, I am not aware if ants have any part in the matter.

 The endangered  Narcissus alcaracensis .

The endangered Narcissus alcaracensis.

Despite their popularity in the garden, many Narcissus are having a hard go of it in the wild. Habitat destruction, climate change, and rampant collecting of wild bulbs are having serious impacts on Narcissus numbers. The IUCN considered at least 5 species to be endangered and a handful of some of the smaller species already thought to be extinct in the wild. In response to some of these issues, protected areas have been established that encompass at least some of the healthy populations that remain for some of these species.

If you are anything like me, you have ignored Narcissus for far too long. Sure, they aren't native to the continent on which I live, and sure, they are one of the most commonly used plants in a garden setting, but every species has a story to tell. I hope that, armed with this new knowledge, you at least take a second look at the Narcissus popping up around your neighborhood. More importantly, I hope this introduction makes you appreciate their wild origins and the fact that we still have much to learn about these plants. I have barely scratched the surface of this genus and there is more more information out there worth perusing. Finally, I hope we can do better for the wild progenitors of our favorite garden plants. They need all the help they can get and unless we start speaking up and working to preserve wild spaces, all that will remain are what we have in our gardens and that is not a future I want to be a part of.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8] [9]

 

Do Yeasts Aid Pollination For the Stinking Hellebore?

Whether they are growing in their native habitat or in some far away garden, Hellebores are some of the earliest plants to bloom in the spring. Hellebore flowers can often be seen blooming long before the snow has melted away. All early blooming plant species are faced with the challenge of attracting pollinators. Though the competition for insect attention is minimal among these early bloomers, only the hardiest insects are out and about on cold, dreary days. It stands to reason then that anything that can entice a potential pollinator would be of great benefit for a plant.

That is why the presence of yeast in the nectar of at least one species of Hellebore has attracted the attention of scientists. The species in question is known scientifically as Helleborus foetidus. The lack of appeal in its binomial is nothing compared to its various common names. One can often find H. foetidus for sale under names like the "stinking hellebore" or worse, "dungwort." All of these have to do with the unpleasant aroma given off by its flowers and bruised foliage. Surprisingly, that is not the topic of this post.

What is more intriguing about the flowers of H. foetidus is that the nectar produced by its smelly green flowers harbors dense colonies of yeast. Yeasts are everywhere on this planet and despite their economic importance, little is known about how they function in nature. For instance, what the heck are these yeast colonies doing in the nectar of this odd Hellebore?

To test this, two researchers from the Spanish National Research Council manipulated yeast colonies within the flowers to see what might be happening. It turns out, yeast in the nectar of H. foetidus actually warms the flowers. As the yeast feed on the sugars within the nectar, their metabolic activity can raise the temperature of the flowers upwards of 2 °C above the ambient. To date, the only other ways in which floral heating has been achieved is either via specific metabolic processes within the floral tissues or by direct heating from the sun. 

In heating the flowers, these yeast colonies may be having serious impacts on the reproductive success of H. foetidus. For starters, these plants are most at home under the forest canopies of central and western Europe. What's more, many populations find themselves growing in the dense shade of evergreens. This completely rules out the ability to utilize solar energy to heat blooms. Additionally, floral heat can mean more visits by potential pollinators. Experiments have shown that bees preferentially visit flowers that are slightly warmer than ambient temperatures. Even the flowers themselves can benefit from that heat. Warmer flowers have higher pollination rates and better seed set.

  Bombus terrestris  was one of the most common floral visitors of  Helleborus foetidus.

Bombus terrestris was one of the most common floral visitors of Helleborus foetidus.

Yeast colonies also have their downsides. The heat generated by the yeast comes from the digestion of sugars. Indeed, nectar housing yeast colonies had drastically reduced sugar loads than nectar without yeast. This has the potential to offset many of the benefits of floral warming in large part because bees are good at discriminating. Bees are visiting these blooms as a food source and by diminishing the sugar loads within the nectar, the yeast may be turning bees off to this potential source. The question then becomes, do bees prefer heat over sugar-rich food? The authors think there might be a trade-off, with bees preferring heated flowers on colder days and sugar-rich flowers on warmer days.

Though the authors found evidence for heating, they did not test for pollinator preference. All we know at this point is that yeast in the nectar significantly warms H. foetidus flowers. Until we know whether bees are making a decision based on yeast colonies, we cannot say whether this is a case of a mutualism or form of parasitism. Such questions will be the subject of future research. Nonetheless, this is a wonderful example of why we need to pay way more attention to the function of yeasts in nature.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

Meet the Ocotillo

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I love the ocotillo (Fouquieria splendens) for many reasons. It is an impossible plant to miss with its spindly, spine-covered stems. It is a lovely plant that is right at home in the arid parts of southwestern North America. Beyond its unique appearance, the ocotillo is a fascinating and important component of the ecology of this region.

My first impression of ocotillo was interesting. I could not figure out where this plant belonged on the tree of life. As a temperate northeasterner, one can forgive my taxonomic ignorance of this group. The family from which it hails, Fouquieriaceae, is restricted to southwestern North America. It contains one genus (Fouquieria) and about 11 species, all of which are rather spiky in appearance.

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Of course, those spines serve as protection. Resources like water are in short supply in desert ecosystems so these plants ensure that it is a real struggle for any animal looking to take a bite. Those spines are tough as well. One manged to pierce the underside of my boot during a hike and I was lucky that it just barely grazed the underside of my foot. Needless to say, the ocotillo is a plant worthy of attention and respect.

One of the most striking aspects of ocotillo life is how quickly these plants respond to water. As spring brings rain to this region of North America, ocotillo respond with wonderful sprays of bright red flowers situated atop their spindly stems. These blooms are usually timed so as to take advantage of migrating hummingbirds and emerging bees. The collective display of a landscape full of blooming ocotillo is jaw-droppingly gorgeous and a sight one soon doesn't forget. It is as if the whole landscape has suddenly caught on fire. Indeed, the word "ocotillo" is Spanish for "little torch."

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Flowering isn't the only way this species responds to the sudden availability of water. A soaking rain will also bring about an eruption of leaves, turning its barren, white stems bright green. The leaves themselves are small and rather fragile. They do not have the tough, succulent texture of what one would expect out of a desert specialist. That is because they don't have to ride out the hard times. Instead, ocotillo are what we call a drought deciduous species, producing leaves when times are good and water is in high supply, and dropping them as soon as the soil dries out.

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This cycle of growing and dropping leaves can and does happen multiple times per year. It is not uncommon to see ocotillo leaf out up to 4 or 5 times between spring and fall. During the rest of the year, ocotillo relies on chlorophyll in its stems for its photosynthetic needs. Interestingly enough, this poses a bit of a challenge when it comes to getting enough CO2. Whereas leaves are covered in tiny pours called stomata which help to regulate gas exchange, the stems of an ocotillo are a lot less porous, making it a challenge to get gases in and out. This is where the efficient metabolism of this plant comes in handy.

All plants undergo respiration like you and me. The carbohydrates made during photosynthesis are broken down to fuel the plant and in doing so, CO2 is produced. Amazingly, the ocotillo (as well as many other plants that undergo stem photosynthesis) are able to recycle the CO2 generated by cellular respiration back into photosynthesis within the stem. In this way, the ocotillo is fully capable of photosynthesis even without leaves.

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Through the good times and the bad, the ocotillo and its relatives are important components of desert ecology. They are as hardy as they are beautiful and getting to see them in person has been a remarkable experience. They ad a flare of surreality to the landscape that must be seen in person to believe.

Further Reading: [1] [2] [3] [4] [5]

From Herbivore to Pollinator Thanks to a Parasitoid

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In the Atlantic forests of Brazil resides a small orchid known scientifically as Dichaea cogniauxiana. Like most plant species, this orchid experiences plenty of pressure from herbivores. It faces rather intense pressures from two species of weevil in the genus Montella. These weevils are new to science and have yet been given full species status. What's more, they don't appear to eat the leaves of D. cogniauxiana. Instead, female weevils lay eggs in the developing fruits and the larvae hatch out and consume the seeds within. In other words, they treat the fruits like a nursery chamber.

This is where this relationship gets interesting. You see, the weevils themselves appear to take matters into their own hands. Instead of waiting to find already pollinated orchids, an event that can be exceedingly rare in the dense Amazonian forests, these weevils go about pollinating the orchids themselves. Females have been observed picking up orchid pollinia and depositing the pollen onto the stigmas. In this way, they ensure that there will be developing fruits in which they can raise their young.

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Left unchecked, the weevil larvae readily consume all of the developing seeds within the pod, an unfortunate blow to the reproductive efforts of this tiny orchid. However, the situation changes when parasitoid wasps enter the mix. The wasps are also looking for a place to rear their young but the wasp larvae do not eat orchid seeds. Instead, the wasps must find juicy weevil larvae in which to lay their eggs. When the wasp larvae hatch out, they eat the weevil larvae from the inside out and this is where things get really interesting.

The wasp larvae develop at a much faster rate than do the weevil larvae. As such, they kill the weevil long before it has a chance to eat all of the orchid seeds. By doing so, the wasp has effectively rescued the orchids reproductive effort. Over a five year period, researchers based out of the University of Campinas found that orchid fruits in which wasp larvae have killed off the weevil larvae produced nearly as many seeds as uninfected fruits. As such, the parasitoid wasps have made effective pollinators out of otherwise destructive herbivorous weevils.

The fact that a third party (in this case a parasitic wasp) can change a herbivore into an effective pollinator is quite remarkable to say the least. It reminds us just how little we know about the intricate ways in which species interact and form communities. The authors note that even though pollination in this case represents selfing and thus reduced genetic diversity, it nonetheless increases the reproductive success of an orchid that naturally experiences low pollination rates to begin with. In the hyper diverse and competitive world of Brazilian rainforests, even self-pollination cab be a boost for this orchid.

Photo Credits: [1] [2]

Further Reading: [1]

Apocynaceae Ant House

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The dogbane family, Apocynaceae, comes in many shapes, sizes, and lifestyles. From the open-field milkweeds we are most familiar with here in North America to the cactus-like Stapeliads of South Africa, it would seem that there is no end to the adaptive abilities of this family. Being an avid gardener both indoors and out, the diversity of Apocynaceae means that I can be surrounded by these plants year round. My endless quest to grow new and interesting houseplants was how I first came to know a genus within the family that I find quite fascinating. Today I would like to briefly introduce you to the Dischidia vines.

 Bullate leaves help the vine clasp to the tree as well as house ant colonies.

Bullate leaves help the vine clasp to the tree as well as house ant colonies.

The genus Dischidia is native to tropical regions of China. Like its sister genus Hoya, these plants grow as epiphytic vines throughout the canopy of warm, humid forests. Though they are known quite well among those who enjoy collecting horticultural curiosities, Dischidia as a whole is relatively understudied. These odd vines do not attach themselves to trees via spines, adhesive pads, or tendrils. Instead, they utilize their imbricated leaves to grasp the bark of the trunks and branches they live upon.

 The odd, bulb-like leaves of the urn vine ( Dischidia rafflesiana )

The odd, bulb-like leaves of the urn vine (Dischidia rafflesiana)

One thing we do know about this genus is that most species specialize in growing out of arboreal ant nests. Ant gardens, as they are referred to, offer a nutrient rich substrate for a variety of epiphytic plants around the world. What's more, the ants will visciously defend their nests and thus any plants growing within.

 The flowers of   Dischidia ovata

The flowers of Dischidia ovata

Some species of Dischidia take this relationship with ants to another level. A handful of species including D. rafflesiana, D. complex, D. major, and D. vidalii produce what are called "bullate leaves." These leaves start out like any other leaf but after a while the edges stop growing. This causes the middle of the leaf to swell up like a blister. The edges then curl over and form a hollow chamber with a small entrance hole.

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These leaves are ant domatia and ant colonies quickly set up shop within the chambers. This provides ample defense for the plant but the relationship goes a little deeper. The plants produce a series of roots that crisscross the inside of the leaf chamber. As ant detritus builds up inside, the roots begin to extract nutrients. This is highly beneficial for an epiphytic plant as nutrients are often in short supply up in the canopy. In effect, the ants are paying rent in return for a place to live.

Growing these plants can take some time but the payoff is worth. They are fascinating to observe and certainly offer quite a conversation piece as guests marvel at their strange form.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1]

Early Land Plants Made The World Muddy

  Cooksonia  is one of the earliest land plants to have evolved.

Cooksonia is one of the earliest land plants to have evolved.

Try to picture the world before life moved onto land. It would have been a vastly different landscape than anything we know today. For one, there would have been no soil. Before life moved onto land, there was nothing organic around to facilitate soil formation. This would have changed as terrestrial habitats were slowly colonized by microbes and eventually plants. A recent paper published in Science is one of the first to demonstrate that the rise in certain sediments on land, specifically mud-forming clays, coincided with the rise in deep-rooted land plants.

This was no small task. The research duo had to look at thousands of reports spanning from the Archean eon, some 3.5 billion years ago, to the Carboniferous period, some 358 million years ago. By looking for the relative amounts of a sedimentary rock called mudrock in terrestrial habitats, they were able to see how the geology of terrestrial habitats was changing through time. What they found was that the presence of mudrock increased by orders of magnitude around the same time as early land plants were beginning to colonize land. Before plants made it onto land, mudrocks comprised a mere 1% of terrestrial sediments. By the end of the Carboniferous period, mudrocks had risen to 26%.

This begs the question, why are mudrocks so significant? What do they tell us about what was going on in terrestrial environments? A key to these questions lies in the composition of mudrocks themselves. Mudrock is made up of fine grained sediments like clay. There are many mechanisms by which clay can be produced and certainly this was going on well before plants made it onto the scene. The difference here is in the quantity of clay-like minerals in these sediments. Whereas bacteria and fungi do facilitate the formation of clay minerals, they do so in small quantities.

 A little bit of moss goes a long way for erosion control!

A little bit of moss goes a long way for erosion control!

The real change came when plants began rooting themselves into the soil. In pushing their roots down into sediments, plants act as conduits for increased weathering of said minerals. Roots not only increase the connectivity between subsurface geology and the atmosphere, they also secrete substances like organic acids and form symbiotic relationships with cyanobacteria and fungi that accelerate the weather process. No purely tectonic or chemical processes can explain the rate of weathering that must have taken place to see such an increase in these fine grained minerals.

What's more, the presence of rooted plants on land would have ensured that these newly formed muds would have stuck around on the landscape much longer. Whereas in the absence of plants, these sediments would have been washed away into the oceans, plants were suddenly holding onto them. Plant roots act as binders, holding onto soil particles and preventing erosion. Aside from their roots, the rest of these early land plants would have also held onto sediments via a process known as the baffling effect. As water and wind pick up and move sediments, they inevitably become trapped in and around the stems and leaves of plants. Even tiny colonies of liverworts and moss are capable of doing this and entire mats of these would have contributed greatly to not only the formation of these sediments, but their retention as well.

The movement of plants onto land changed the course of history. It was the beginning of massive changes to come and much of that started with the gradual formation of soils. We owe everything to these early botanical pioneers.

Photo Credit: [1]

Further Reading: [1]

The Mighty Saguaro Cactus

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Where does one begin with a plant like the saguaro cactus (Carnegiea gigantea)? It is recognized the world over for its iconic appearance yet its native range is disproportionately small compared to its popularity. It is easily one of the most spectacular plants I have ever encountered and I will never forget the sound the wind makes as it blows over its spiny pleated trunk. It would be impossible to sum up our collective knowledge of this species in one article, however, I feel that some form of an introduction is necessary. Today I want to honor this icon of the Sonoran Desert.

The saguaro is the only member of the genus Carnegiea, which is part of a subtribe of cacti characterized by their columnar appearance. Despite its unique taxonomic affinity, the evolutionary origins of this cactus remains a bit of a mystery. Though it is undoubtedly related to other columnar cacti of the Americas, a proper family tree seems to be just out of our reach. Due to lots of convergent and parallel evolution as well as conflicts between genealogies and species histories, we still aren't sure of its evolutionary origins. What we do know about this species on a genetic level is nonetheless quite interesting. For instance the saguaro has one of the smallest chloroplast genomes of any non-parasitic plant and we aren’t exactly sure why this is the case.

Saguaro are long lived cacti. Estimating age of a cactus can be rather tricky considering that they don’t produce annual growth rings. This is where long term monitoring projects have come in handy. By observing hundreds of saguaro throughout the Sonoran Desert, experts believe that saguaro can regularly reach ages of 150 to 170 years and some individuals may be able to live for more than 200 years. Amazingly, it is thought that saguaro will not begin to grow their characteristic arms until they reach somewhere around 50 to 100 years of age. That being said, some saguaro never bother growing arms. It all depends on where the conditions they experience throughout their lifetime.

Growth for a saguaro depends on where they are rooted. Under favorable conditions, a saguaro can grow to heights of 50 feet or more, with the world record holder clocking in at a whopping 78 feet in height. Such growth becomes all the more impressive when you realize just how agonizingly slow the process can be. Studies have shown that juvenile saguaro only put on about 1.5 inches of growth in their first eight years of life.

Despite preconceived notions about the hardy nature of most cacti, saguaro have proven to be rather specific in their needs. They are limited in their growth and distribution by the availability of water and warm temperatures. Saguaro, especially young individuals, cannot tolerate periods of prolonged frost. Additionally, germination and seedling survival occur most frequently only during the wettest years. In fact, one study showed that successful years for reproduction in these beloved cacti were tied to volcanic eruptions that cooled the climate just enough to allow the young saguaro to become established.

Outside of volcanic eruptions, saguaro appear to have friends in the surrounding vegetation. Studies have shown that saguaro seedlings seem to do best when growing under the shade of trees like the palo verde (Parkinsonia florida), ironwood (Olneya tesota), and mesquite (Prosopis velutina). The microclimates produced by these trees are much more favorable for saguaro growth than are open desert conditions. In essence, these trees serve as nurseries for young saguaro until they are large enough to handle more exposed conditions. Their nursery habits are not mutually beneficial however as research suggests that saguaro eventually compete with the trees that once protected them for precious resources like nutrients and water.

 Saguaros outgrowing their palo verde nurse tree. 

Saguaros outgrowing their palo verde nurse tree. 

At roughly 35 years of age, a saguaro will begin to flower. Flowers are small compared to the size of the cactus but they are abundant. Most flowers are produced at the apex of the cactus and it is thought that the growth of saguaro arms is largely a way of increasing the reproductive potential of large individuals. The flowers are cream colored and night scented. They open in the evening but will stay open and continue to produce nectar well into the morning hours.

Though a wide variety of animals will visit these flowers, the main pollinators are bees during the day and lesser long-nosed bats at night. Interestingly, it has been found that certain amino acids within the nectar of the saguaro can actually help female bats sustain lactation while raising their young, making them a valuable food source for these flying mammals. Catering to such a broad spectrum of potential pollinators is thought to have evolved as a means of increasing seed set. Each saguaro ovary contains many ovules and the more pollen that makes it onto the stigma, the more seeds will be produced.

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 A lesser long-nosed bat pollinates a saguaro bloom.

A lesser long-nosed bat pollinates a saguaro bloom.

Due to their size and abundance, it is easy to understand why the saguaro is such an ecologically important species in the Sonoran Desert ecosystem. In essence, they function similar to trees in that they serve as vital sources of shelter and food for myriad desert animals. Woodpeckers, especially the gila and the gilded flicker, regularly hollow out and build nests in saguaro trunks. These hollows are subsequently used by many different bird, mammal, and reptile species. The flowers and fruits are important sources of food for wildlife.

 Gila woodpecker with its nesting hole.

Gila woodpecker with its nesting hole.

 Gila woodpecker holes become homes for other birds like owls. 

Gila woodpecker holes become homes for other birds like owls. 

 On rare occasions, woodpecker holes can even become home to other cacti!

On rare occasions, woodpecker holes can even become home to other cacti!

I sincerely hope that this brief introduction does at least some justice to the wonderful organism that is the saguaro cactus. The Sonoran Desert would be a shell of an ecosystem without its presence. What’s more, it has played a significant role in the culture of this region for millennia. Though it appears quite numerous on the landscape, the long-term status of the saguaro is cause for concern. Numerous declines have been reported throughout its range. With its slow growth rates and infrequent recruitment events, the saguaro can be quite sensitive to rapid changes in its environment. Luckily it has received special protection laws throughout its US range.

Photo Credits: [1] [2] [3] [4]


Further Reading: [1] [2] [3] [4] [5] [6] [7] [8] [9] 

The Wild World of the Creosote Bush

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Apart from the cacti, the real rockstar of my Sonoran experience was the creosote bush (Larrea tridentata). Despite having been quite familiar with creosote as an ingredient, I admit to complete ignorance of the plant from which it originates. Having no familiarity with the Sonoran Desert ecosystem, I was walking into completely new territory in regard to the flora. It didn’t take long to notice creosote though. Once we hit the outskirts of town, it seemed to be everywhere.

If you are in the Mojave, Sonoran, and Chihuahuan Deserts of western North America, you are never far from a creosote bush. They are medium sized, slow growing shrubs with sprays of compact green leaves, tiny yellow flowers, and fuzzy seeds. Apparently what is thought of as one single species is actually made up of three different genetic populations. The differences between these has everything to do with chromosome counts. Populations in the Mojave Desert have 78 chromosomes, Sonoran populations have 52 chromosomes, and Chihuahuan have 26. This may have to do with the way in which these populations have adapted to the relative amounts of rainfall each of these deserts receive throughout the year, however, it is hard to say for sure.

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Regardless, creosote is supremely adapted to these xeric ecosystems. For starters, their branching architecture coupled with their tiny leaves are arranged so as to make the most out of favorable conditions. If you stare at these shrubs long enough, you may notice that their branches largely orient towards the southeast. Also, their leaves tend to be highly clustered along the branches. It is thought that this branching architecture allows the creosote to minimize water loss while maximizing photosynthesis.

Deserts aren’t hot 24 hours per day. Night and mornings are actually quite cool. By taking advantage of the morning sun as it rises in the east, creosote are able to open their stomata and commence photosynthesis during those few hours when evapotranspiration would be at its lowest. In doing so, they are able to minimize water loss to a large degree. Although their southeast orientation causes them to miss out on afternoon and evening sun to a large degree, the benefits of saving precious water far outweigh the loss to photosynthesis. The clustering of the leaves along the branches may also reduce overheating by providing their own shade. Coupled with their small size, this further reduces heat stress and water loss during the hottest parts of the day.

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Creosote also secrets lots of waxy, resinous compounds. These coat the leaves and to some extent the stems, making them appear lacquered. It is thought that this also helps save water by reducing water loss through the leaf cuticle. However, the sheer diversity of compounds extracted from these shrubs suggests other functions as well. It is likely that at least some of these compounds are used in defense. One study showed that when desert woodrats eat creosote leaves, the compounds within caused the rats to lose more water through their urine and feces. They also caused a reduction in the amount of energy the rats were able to absorb from food. In other words, any mammal that regularly feeds on creosote runs the risk of both dehydration and starvation. This isn’t the only interesting interaction that creosote as with rodents either. Before we get to that, however, we first need to discuss roots.

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Creosote shrubs have deep root systems that are capable of accessing soil water that more shallowly rooted plants cannot. This brings them into competition with neighboring plants in intriguing ways. When rainfall is limited, shallowly rooted species like Opuntia gain access to water before it has a chance to reach deeper creosote roots. Surprisingly this happens more often than you would think. The branching architecture of creosote is such that it tends to accumulate debris as winds blow dust around the desert landscape. As a result, the soils directly beneath creosote often contain elevated nutrients. This coupled with the added shade of the creosote canopy means that seedlings that find themselves under creosote bushes tend to do better than seedlings that germinated elsewhere. As such, creosote are considered nurse plants that actually facilitate the growth and survival of surrounding vegetation. So, if recruitment and resulting competition from vegetation can become such an issue for long term creosote survival, why then do we still so much creosote on the landscape?

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The answer may lie in rodents and other burrowing animals in these desert ecosystems. Take a look at the base of a large creosote and you will often find the ground littered with burrows. Indeed, many a mammal finds the rooting zone of the creosote shrub to be a good place to dig a den. When these animals burrow under shallowly rooted desert plants, many of them nibble on and disturb the rooting zones. Over the long-term, this can be extremely detrimental for the survival of shallow rooted species. This is not the case for creosote. Its roots run so deep that most burrowing animals cannot reach them. As such, they avoid most of the damage that other plants experience. This lends to a slight survival advantage for creosote at the expense of neighboring vegetation. In this way, rodents and other burrowing animals may actually help reduce competition for the creosote.

Barring major disturbances, creosote can live a long, long time. In fact, one particular patch of creosote growing in the Mojave Desert is thought to be one of the oldest living organisms on Earth. As creosote shrubs grow, they eventually get to a point in which their main stems break and split. From there, they begin producing new stems that radiate out in a circle from the original plant. These clones can go on growing for centuries. By calculating the average growth rate of these shrubs, experts have estimated that the Mojave specimen, affectionately referred to as the “King Clone,” is somewhere around 11,700 years old!

 The ring of creosote that is King Clone.

The ring of creosote that is King Clone.

For creosote, its slow and steady wins the race. They are a backbone of North American desert ecosystems. Their structure offers shelter, their seeds offer food, and their flowers support myriad pollinators. Creosote is one shrub worthy of our respect and admiration.

Photo Credit: [1] [2]

Further Reading: [1] [2] [3] [4]