A Pair of Cycads Aim to Reproduce in the UK for the First Time in 120 Million Years

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We tend to speak in the future tense when it comes to climate change. Phrases like "climate change will alter..." and "species will be affected by climate change..." suggest that these are issues we will eventually face at some point down the road. In reality, climate change is happening and life is already responding. Plants are some of the best indicators that thing are and have been changing since humans started wreaking havoc on natural systems.

Even in the most remote corners of our planet, where human presence is almost nil, we are finding evidence of climate change in the flora. For instance, deep in the Andes Mountains, trees are already adjusting their ranges to cope with changes in regional climate. And now, cycads are reproducing outdoors in the UK for the first time since dinosaurs walked the Earth.

Sago palms (Cycas revoluta) are native to parts of southern Japan and though they can handle frosts, they require mild winters and hot summers to successfully reproduce. A few decades ago, one would have a hard time trying to overwinter these cycads outdoors in the UK but the climate has been changing. Today, these plants can be successfully grown outdoors in the southern portion of the country provided they are given a little bit of shelter. Though they will grow well in such situations, convincing these plants to reproduce is another matter entirely.

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The UK is no stranger to the effects of climate change. For instance, the plants in question are growing in the Ventnor Botanic Garden on the Isle of Wight where even today’s lowest temperatures are significantly hotter than even the hottest recorded temperatures on the island 100 years ago. The plants are responding accordingly.

For the first time in UK’s human history, both male and female sago palm cycads are producing cones at the same time outdoors. This means that cycads will be able to successfully reproduce at this latitude since at least the Cretaceous Period, roughly 120 million years ago. During the Cretaceous, distant cousins of these cycads could be found growing in what today is the UK. At that time, Earth’s atmosphere was chock full of CO2 and quite hot. The fact that cycads are once again able to reproduce in the UK is alarming to say the least. It is a forecast of more changes to come.

UPDATE: Thanks to Dr. Susannah Lyndon and Robbie Blackhall-Miles for bringing to my attention that this is actually not this first time this has happened in the UK. Apparently Sago palm cycads have produced cones in places like London in recent history. Nonetheless, such events are evidence of a warming climate.

Photo Credits: [1] [2]

Further Reading: [1] [2]

Surprising Genetic Diversity in Old Growth Trees

Long-lived trees face a lot of challenges throughout their lives. Many trees can live for centuries, which can be a problem because plants cannot get up and move when conditions become unfavorable. This should equate to a slower rates of adaptation and evolution for long lived trees but that isn’t always the case. Many trees are often superbly capable of adapting to local conditions. Recently, a team of researchers from the University of British Columbia have provided some insights into the genetic mechanisms that may underpin such adaptive potential.

Genetic insights came from a species of conifer many will be familiar with - the Sitka spruce (Picea sitchensis). Researchers were interested in these trees because they live for a long time (upwards of 500 years or more) and can grow to heights of over 70 meters (230 ft.). They wanted to understand how genetic mutations work in trees like the Sitka spruce because plants are doing things a bit different than animals in that department.

Plants are modular organisms, meaning they grow by producing multiple copies of discrete units. This equates to a branching structure whose overall shape is in large part determined by environmental influences. It also means that when genetic mutations occur in one branch, they can be carried on throughout the growth of those tissues independent of what is going on throughout the rest of the plant. This means that older trees can often accumulate a surprising amount of genetic diversity throughout the entire body of the plant.

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When researchers sampled the DNA of tissues from the trunks and the needles of tall, old growth Sitka spruce, they were shocked by what they had found. From the base of the tree to the needles in the canopy, an old growth Sitka spruce can show as much as 100,000 genetic differences. That is a lot of genetic diversity for a single organism. Though plenty of other trees have been found to exhibit varying levels of genetic differences within individuals, this is one of the highest mutation rates ever found in a single eukaryotic organism. This could also explain why such long-lived organisms can survive in a changing world for their entire lives.

Now, it is important to note that many mutations are likely either neutral or potentially harmful. Also, the rates of mutation may differ depending on where you look on this tree. For instance, needles at the top of a Sitka spruce are going to be exposed to far more gene-altering UV radiation than bark tissues near the base. Still, over the lifetime of a single tree, rare beneficial mutations can and do accumulate. Imagine a scenario in which one branch mutation results in needles that are more resistant to say an insect pest. Those needles could hypothetically receive less damage than needles elsewhere on the tree. This odd form of selection is occurring within the lifetime of that tree and may even have implications for the future offspring of that tree thanks again to the quirks of how tree reproductive cells develop.

Many trees also do not have segregated germlines. What this means is that unlike animals whose reproductive cells develop from separate cell lineages than the rest of their body cells, the reproductive cells of trees develop from somatic cells, which are the same cells that form stems, leaves, and branches. This means that if a mutation occurs on the germline of a branch that eventually goes on to produce cones, these mutations can be passed on in the seeds of those cones. This obviously needs a lot of evidence to substantiate but now that a mechanism is in place, we know where and what to look for.

Photo Credits: [1] [2]

Further Reading: [1] [2]

A Herbaceous Conifer From the Triassic

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It is hard to make broad generalizations about groups of related organisms. There are always exceptions to any rule. Still, there are some “facts” we can throw around that seem to apply pretty well to specific branches on the tree of life. For instance, all of the gymnosperm lineages we share our planet with today are woody, relatively slow to reach sexual maturity, and are generally long-lived. This has not always been the case. Fossil discoveries from France suggest that in the past, gymnosperms were experimenting with a more herbaceous lifestyle.

The fossils in question were discovered in eastern France back in the 1800’s. The strata from which they were excavated dates back to the Middle Triassic, some 247 million years ago. Immortalized in these rocks were numerous spindly plants with strap-like leaves and a few branches, each ending in what look like tiny cones. Early interpretations suggested that these may represent an extinct lycopod, however, further investigation suggested something very surprising - a conifer with an herbaceous growth habit.

Indeed, thanks to even more scrutiny, it is now largely agreed upon that what was preserved in these rocks were essentially herbaceous conifers. The fossils were given the name Aethophyllum stipulare. They are wonderfully complete, depicting roots, shoots, leaves, and reproductive organs. Moreover, the way in which they were fossilized preserved lots of fine-scale anatomical details. Taken together, there are plenty of clues available that allow paleobotanists to say a lot about how this odd conifer made a living.

For starters, they were not very big plants. Not a single specimen has been found that exceeds 2 meters (6.5 ft) in height. The main stem of these conifers only seem to branch a couple of times. Cones were formed at the tips of the upper branches and not a single specimen has been found that depicts subsequent growth following cone formation. This suggests that Aethophyllum exhibited determinate growth, meaning that individuals grew to a certain size, reproduced, and did not continue to grow after that. Female cones were situated at the tips of the upper most branches and male cones were situated at the tips of lower shoots. The smallest reproductive individuals that have been unearthed are only 30 cm (11 in) in height, which suggests that Aethophyllum  was capable of reproducing within a few months of germination.

Artists reconstruction of  Aethophyllum stipulare

Artists reconstruction of Aethophyllum stipulare

Amazingly, researchers were also able to extract fossilized pollen and seeds from some of the Aethophyllum cones. The pollen itself is saccate, much like what we see in many extant conifers. By comparing the morphology of the pollen extracted from the cones to other fossil pollen records, researchers now feel confident that Aethophyllum is the source of pollen grains discovered in sediments from western, central, and southern Europe, Russia, Northern Africa, and China, suggesting that Aethophyllum was pretty wide spread during the Middle Triassic. Aethophyllum seeds were small, ellipsoid, and were not winged, likely germinating a short distance from the parent.

The stems of Aethophyllum are interesting in the own right. Thanks to their preservation, cross sections have been made and they reveal that these plants only ever produced secondary tracheids and primary xylem. The only place on the plant where any signs of woody secondary xylem occur are at the base of the cones. This adds further confirmation that Aethophyllum was herbaceous at the onset of sexual maturity.

Another intriguing aspect of the stem is the presence of numerous large air spaces within the stem pith. Today, this anatomical feature is present in plants like bamboo, Equisetum, and the flowering stalks of Agave, all of which exhibit alarmingly fast growth rates for plants. This suggests that not only did Aethophyllum reproduce early in its life, it also likely grew extremely fast.

1. Smallest fertile plant in the Grauvogel and Gall collections, with two stems extending from the root, and terminal ovulate cone (OC) on one branch (scale bar=10 cm). 2. Cross-section of stem in the Grauvogel and Gall collections showing cauline bundles with scanty wood (at left, top and right) surrounding large pith with large, aerenchymatous lacunae and interspersed pith parenchyma cells. Vascular cambium, phloem, and more peripheral tissues are not preserved (scale bar=200 μm). 3.Seedling in the Grauvogel and Gall collections showing primary root (R), cotyledons (C) and stem (S) with apically borne leaves (scale bar=10 cm).  Quoted from SOURCE

1. Smallest fertile plant in the Grauvogel and Gall collections, with two stems extending from the root, and terminal ovulate cone (OC) on one branch (scale bar=10 cm). 2. Cross-section of stem in the Grauvogel and Gall collections showing cauline bundles with scanty wood (at left, top and right) surrounding large pith with large, aerenchymatous lacunae and interspersed pith parenchyma cells. Vascular cambium, phloem, and more peripheral tissues are not preserved (scale bar=200 μm). 3.Seedling in the Grauvogel and Gall collections showing primary root (R), cotyledons (C) and stem (S) with apically borne leaves (scale bar=10 cm). Quoted from SOURCE

Mature Aethophyllum aren’t the only fossils available either. Many seedlings have been discovered in close proximity to the adults. Seedlings were also exquisitely preserved, depicting hypocotyl, a primary root system, two two-veined cotyledons, and a short stem with four-veined leaves arranged in a helix. The fact that seedlings and adults were found in such close proximity lends to the idea that Aethophyllum populations were made up of multi-aged stands, not unlike some of the early successional plants we find in disturbed habitats today.

The sediments in which these plants were fossilized can also tell us something about the habitats in which Aethophyllum grew. The rock layers are made up of a mix of sediments typical of what one would find in a flood plain or delta. Also, Aethophyllum aren’t the only plant remains discovered. Many species known to grow in regularly disturbed, flood-prone habitats have also been found. Taken together these lines of evidence suggest that Aethophyllum was similar to what we would expect from herbaceous plants growing in similar habitats today. They grew fast, reproduced early, and had to jam as many generations in before the next flood ripped through and hit the reset button.

Aethophyllums small size, lack of wood, and rapid growth rate all point to a ruderal lifestyle. Today, this niche is largely filled by angiosperms. No conifers alive today can claim such territories. The discovery of Aethophyllum demonstrates that this was not always the case. The fact that pollen has been found far outside of France suggests that this ruderal lifestyle worked quite well for Aethophyllum.

The terrestrial habitats of the Middle Triassic were dominated by the distant relatives of modern day ferns, lycophytes, and gymnosperms. Needless to say, it was a very different world than anything that we are familiar with today. However, that does not mean that the pressures of natural selection were necessarily different. Aethophyllum is evidence that specific selection pressures, in this case regular flood disturbance, select for similar traits in plants through time. Why Aethophyllum went extinct is anyone’s guess. Despite how well they have been preserved, there is still a lot of mystery surrounding this plant.

Photo Credit: [1]

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



The Celery-Topped Conifers

I am only just starting to fully appreciate the diversity in form and habit exhibited by the gymnosperm lineages alive today. What I once thought of as a unidimensional group of plants is proving to be wonderfully diverse, despite being overshadowed by the angiosperms. For instance, imagine my surprise when I first laid eyes on a member of the genus Phyllocladus.

At first glance, these weird conifers look more like a broad-leaf angiosperm. This similarity is superficial, of course. Before we get to why they look the way they do, it is worth considering this group from a as a whole. The genus Phyllocladus comprises roughly 5 species spread out among New Zealand, Tasmania, and Malesia. They are somewhat variable in form but usually settle out somewhere between a good sized shrub and a medium sized tree. Where exactly this genus of oddball gymnosperms fits on the tree of life is subject to some debate.

Phyllocladus aspleniifolius

Phyllocladus aspleniifolius

Phyllocladus trichomanoides

Phyllocladus trichomanoides

For many years after its initial description, Phyllocladus was placed in a family of its own - Phyllocladaceae. Subsequent molecular work has only managed to add to the confusion. Despite its unique morphological characteristics, some authors feel this genus fits nicely into the family Podocarpaceae. At least one other study suggests that it doesn’t belong in Podocarpaceae but rather is situated as sister to the family. By the looks of it, this will not be cleared up any time soon. So, for now, let’s focus in on why these plants are so strange.

For starters we have the “leaves.” I place the word ‘leaves’ in quotes because they are not true leaves. The correct term for these structures are phylloclades (hence the generic name). A phylloclade is a flattened projection of a branch that takes on the form and function of a leaf. What we know of as leaves have been greatly reduced in the genus Phyllocladus. If you want to see them, you must look closely at the tips of the phylloclades. Early on in their development, the leaves exist as tiny brown scales. These scales are gradually lost over time as they serve no function for the plant.

Phyllocladus alpinus

Phyllocladus alpinus

Phyllocladus hypophyllus

Phyllocladus hypophyllus

Though no one has tested this directly (that I am aware of), the evolution of phylloclades over leaves likely has to do with energy conservation in one form or another. Why produce stems and leaves when you can co-opt stem-like structures to do the work for you? Oddly enough, some suggest that to consider them stems in the truest sense of the word is erroneous. Morphologically speaking, they share traits that are intermediate between branches and stems. However, I am going to need to do more homework before I feel comfortable elaborating on this point.

Only when it comes time for reproduction does their place among the gymnosperms become readily apparent, that is before the ovules are fertilized. All members of the genus Phyllocladus produce cones. Male cones are tiny, cylindrical structures located at the ends of their side branches whereas female cones are clustered into groups along the axils or margins of the phylloclades. Once fertilized, however, these plants offer another point of confusion for the casual observer.

The fleshy “fruits” of  Phyllocladus aspleniifolius

The fleshy “fruits” of Phyllocladus aspleniifolius

Phyllocladus is yet another genus of conifers that has converged on a fruit-like seed dispersal strategy. As the seed cones mature, the scales gradually swell and become berry-like. Poking out of the bright red and/or white aril is a single seed. These fleshy arils function in a similar way to fruit in that they attract birds, which then consume them, dispersing the seeds later on in their feces.

Another intriguing aspect of their morphology occurs below ground. The roots of this genus form nodules, which provide a home for bacteria that specializing in fixing atmospheric nitrogen. In return for a home and some carbohydrates from photosynthesis, these bacteria pay these trees with nitrogen that would otherwise be unavailable. Pretty remarkable stuff for a such an esoteric group of conifers!

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Photo Credits: [1] [2]

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

The Japanese Umbrella Pine

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My first impression of the Japanese umbrella pine was that I was looking at a species of yew (Taxus spp.). Sure, its features were a bit more exaggerated than I was used to but what do I know? Trying to understand tree diversity is a recent development in my botanical obsession so I don’t have much to base my opinions on. Regardless, I am glad I gave the little sapling I was looking at a closer inspection. Turns out, the Japanese umbrella pine is most definitely not a yew. It is actually unique in its taxonomic position as the only member of the family Sciadopityaceae.

The Japanese umbrella pine goes by the scientific name of Sciadopitys verticillata. Both common and scientific names hint at the whorled arrangements of its “leaves.” I place leaves in quotes because they are not leaves at all. One of the most remarkable features of this tree is the fact that those whorled leaves are actually thickened, photosynthetic extensions of the stem known as “cladodes.”

Those tiny bumps along the stems are actually highly reduced leaves whereas the whorls of photosynthetic “leaves” are actually modified extensions of the stem called “cladodes.”

Those tiny bumps along the stems are actually highly reduced leaves whereas the whorls of photosynthetic “leaves” are actually modified extensions of the stem called “cladodes.”

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It seems that the true leaves of the Japanese umbrella pine have, through evolutionary time, been reduced to tiny, brown scales that clasp the stems. I am not sure what evolutionary advantage(s) cladodes infer over leaves, however, at least one source suggested that cladodes may have fewer stomata and therefore can help to reduce water loss. Until someone looks deeper into this mystery, we cannot say for sure.

As a tree, the Japanese umbrella pine is slow growing. Records show that young trees can take upwards of a decade to reach average human height. However, given time, the Japanese umbrella pine can grow into an impressive specimen. In the forests of Japan, it is possible to come across trees that are 65 to 100 ft (20 – 35 m) tall. It was once wide spread throughout much of southern Japan, however, an ever-increasing human population has seen that range reduced.

A 49.5 million years old fossil of a  Sciadopitys  cladode.

A 49.5 million years old fossil of a Sciadopitys cladode.

The gradual reduction of this species is not solely the fault of humans. Fossil evidence shows that the genus Sciadopitys was once wide spread throughout parts of Europe and Asia as well. Whereas the current diversity of this genus is limited to a single species, fossils of at least three extinct species have been found in rocks dating back to the Triassic Period, some 230 million years ago. It would appear that this obscure conifer family, like so many other gymnosperm lineages, has been on the decline for quite some time.

Despite the obscure strangeness of the Japanese umbrella tree, it has gained considerable popularity as a unique landscape tree. Because it hails from a relatively cool regions of Japan, the Japanese umbrella tree adapts quite well to temperate climates around the globe. Enough people have grown this tree that some cultivars even exist. Whether you see it as a specimen in an arboretum or growing in the wild, know that you are looking at something quite special. The Japanese umbrella tree is a throwback to the days when gymnosperms were the dominant plants on the landscape and we are extremely lucky that it made it through to our time.

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

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

Gymnosperms and Fleshy "Fruits"

Fleshy red aril surrounding the seeds of  Taxus baccata.

Fleshy red aril surrounding the seeds of Taxus baccata.

Many of us were taught in school that one of the key distinguishing features between gymnosperms and angiosperms is the production of fruit. Fruit, by definition, is a structure formed from the ovary of a flowering plant. Gymnosperms, on the other hand, do not enclose their ovules in ovaries. Instead, their unfertilized ovules are exposed (to one degree or another) to the environment. The word “gymnosperm” reflects this as it is Greek for “naked seed.” However, as is the case with all things biological, there are exceptions to nearly every rule. There are gymnosperms on this planet that produce structures that function quite similar to fruits.

Cross section of a  Ginkgo  ovule with red arrow showing the integument.  Photo copyright Bruce Kirchoff, Licensed under CC-BY

Cross section of a Ginkgo ovule with red arrow showing the integument.

Photo copyright Bruce Kirchoff, Licensed under CC-BY

The key to understanding this evolutionary convergence lies in understanding the benefits of fruits in the first place. Fruits are all about packing seeds into structures that appeal to the palates of various types of animals who then eat said fruits. Once consumed, the animals digest the fruity bits and will often deposit the seeds elsewhere in their feces. Propagule dispersal is key to the success of plants as it allows them to not only to complete their reproductive cycle but also conquer new territory in the process. With a basic introduction out of the way, let’s get back to gymnosperms.

“Fruits” of  Cephalotaxus fortunei  (Cephalotaxaceae)

“Fruits” of Cephalotaxus fortunei (Cephalotaxaceae)

There are 4 major gymnosperm lineages on this planet - the Ginkgo, cycads, gnetophytes, and conifers. Each one of these groups contains members that produce fleshy structures around their seeds. However, their “fruits” do not all develop in the same way. The most remarkable thing to me is that, from a developmental standpoint, each lineage has evolved its own pathway for “fruit” production.

Ginkgo  “fruits” are full of butyric acid and smell like rotting butter or vomit.

Ginkgo “fruits” are full of butyric acid and smell like rotting butter or vomit.

For instance, consider ginkgos and cycads. Both of these groups can trace their evolutionary history back to the early Permian, some 270 - 280 million years ago, long before flowering plants came onto the scene. Both surround their developing seed with a layer of protective tissue called the integument. As the seed develops, the integument swells and becomes quite fleshy. In the case of Ginkgo, the integument is rich in a compound called butyric acid, which give them their characteristic rotten butter smell. No one can say for sure who this nasty odor originally evolved to attract but it likely has something to do with seed dispersal. Modern day carnivores seem to be especially fond of Ginkgo “fruits,” which would suggest that some bygone carnivore may have been the main seed disperser for these trees.

“Fruits” contained within the female cone of a cycad ( Lepidozamia peroffskyana ).

“Fruits” contained within the female cone of a cycad (Lepidozamia peroffskyana).

The Gnetophytes are represented by three extant lineages (Gnetaceae, Welwitschiaceae, and Ephedraceae), but only two of them - Gnetaceae and Ephedraceae - produce fruit-like structures. As if the overall appearance of the various Gnetum species didn’t make you question your assumptions of what a gymnosperm should look like, its seeds certainly will. They are downright berry-like!

Berry-like seeds of  Gnetum gnemon .

Berry-like seeds of Gnetum gnemon.

The formation of the fruit-like structure surrounding each seed can be traced back to tiny bracts at the base of the ovule. After fertilization, these bracts grow up and around the seed and swell to become red and fleshy. As you can imagine, Gnetum “fruits” are a real hit with animals. In the case of some Ephedra, the “fruit” is also derived from much larger bracts that surround the ovule. These bracts are more leaf-like at the start than those of their Gnetum cousins but their development and function is much the same.

Red, fleshy bracts of  Ephedra distachya .

Red, fleshy bracts of Ephedra distachya.

Whereas we usually think of woody cones when we think of conifers, there are many species within this lineage that also have converged on fleshy structures surrounding their seeds. Probably the most famous and widely recognized example of this can be seen in the yews (Taxus spp.). Ovules are presented singly and each is subtended by a small stalk called a peduncle. Once fertilized, a group of cells on the peduncle begin to grow and differentiate. They gradually swell and engulf the seed, forming a bright red, fleshy structure called an “aril.” Arils are magnificent seed dispersal devices as birds absolutely relish them. The seed within is quite toxic so it usually escapes the process unharmed and with any luck is deposited far away from the parent plant.

The berry-like cones of  Juniperus communis .

The berry-like cones of Juniperus communis.

Another great example of fleshy conifer “fruits” can be seen in the junipers (Juniperus spp.). Unlike the other gymnosperms mentioned here, the junipers do produce cones. However, unlike pine cones, the scales of juniper cones do not open to release the seeds inside. Instead, they swell shut and each scale becomes quite fleshy. Juniper cones aren’t red like we have seen in other lineages but they certainly garnish the attention of many a small animal looking for food.

I have only begun to scratch the surface of the fruit-like structures in gymnosperms. There is plenty of literary fodder out there for those of you who love to read about developmental biology and evolution. It is a fascinating world to uncover. More importantly, I think the fleshy “fruits” of the various gymnosperm lineages stand as a testament to the power of natural selection as a driving force for evolution on our planet. It is amazing that such distantly related plants have converged on similar seed dispersal mechanisms by so many different means.

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

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

The Tecate Cypress: A Tree Left Hanging in the Balance

The tecate cypress is a relict. Its tiny geographic distribution encompasses a handful of sights in southern California and northwestern Mexico. It is a holdover from a time when this region was much cooler and wetter than it is today. It owes its survival and persistence to a combination of toxic soils, a proper microclimate, and fires that burn through every 30 to 40 years. However, things are changing for the Tecate cypress and they are changing fast. The fires that once ushered in new life for isolated populations of this tree are now so intense that they may spell disaster.

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The taxonomy of the Tecate cypress has undergone a few revisions since it was first described. Early work on this species suggested it was simply a variety of Cupressus guadalupensis. Subsequent genetic testing revealed that these two trees were distinct enough to each warrant species status of their own. It was then given the name Cupressus forbesii, which will probably be familiar to most folks who know it well. Work done on the Tecate cypress back in 2012 has seen it moved out of the genus Cupressus and into the genus Hesperocyparis. As far as I am concerned, whether you call it Cupressus forbesii or Hesperocyparis forbesii matters not at this point.

The Tecate cypress is an edaphic endemic meaning it is found growing only on specific soil types in this little corner of the continent. It appears to prefer soils derived from ultramafic rock. The presence of high levels of heavy metals and low levels of important nutrients such and potassium and nitrogen make such soils extremely inhospitable to most plants. As such, the Tecate cypress experiences little competition from its botanical neighbors. It also means that populations of this tree are relatively small and isolated from one another.

The Tecate cypress also relies on fire for reproduction. Its tiny cones are serotinous, meaning they only open and release seeds in response to a specific environmental trigger. In this case, its the heat of a wildfire. Fire frees up the landscape of competition for the tiny Tecate cypress seedlings. After a low intensity fire, literally thousands of Tecate cypress seedlings can germinate. Even if the parent trees burn to a crisp, the next generation is there, ready to take their place.

At least this is how it has happened historically. Much has changed in recent decades and the survival of these isolated Tecate cypress populations hangs in the balance. Fires that once gave life are now taking it. You see, decades of fire suppression have changed that way fire behaves in this system. With so much dry fuel laying around, fires burn at a higher intensity than they have in the past. What's more, fires sweep through much more frequently today than they have in the past thanks to longer and longer droughts.

Taken together, this can spell disaster for small, isolated Tecate cypress populations. Even if thousands of seedlings germinate and begin to grow, the likelihood of another fire sweeping through within a few years is much higher today. Small seedlings are not well suited to cope with such intense wildfires and an entire generation can be killed in a single blaze. This is troubling when you consider the age distributions of most Tecate cypress stands. When you walk into a stand of these trees, you will quickly realize that all are of roughly the same age. This is likely due to the fact that they all germinated at the same time following a previous fire event.

If all reproductive individuals come from the same germination event and wildfires are now killing adults and seedlings alike, then there is serious cause for concern. Additionally, when we lose populations of Tecate cypress, we are losing much more than just the trees. As with any plant, these trees fit into the local ecology no matter how sparse they are on the landscape. At least one species of butterfly, the rare Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress. Without this tree, their larvae have nothing to feed on.

Thorne's hairstreak ( Callophrys gryneus thornei ), lays its eggs only on the scale-like leaves of the Tecate cypress.

Thorne's hairstreak (Callophrys gryneus thornei), lays its eggs only on the scale-like leaves of the Tecate cypress.

Although things in the wild seem uncertain for the Tecate cypress, there is reason for hope. Its lovely appearance and form coupled with its unique ecology has led to the Tecate cypress being something of a horticultural curiosity in the state of California. Seeds are easy enough to germinate provided you can get them out of the cones and the trees seem to do quite well in cultivation provided competition is kept to a minimum. In fact, specimen trees seem to adapt quite nicely to California's cool, humid coastal climate. Though the future of this wonderful endemic is without a doubt uncertain, hope lies in those who care enough to grow and cultivate this species. Better management practices regarding fire and invasive species, seed collection, and a bit more public awareness may be just what this species needs.

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

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

Cycad Pollinators

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When it comes to insect pollination, flowering plants get all of the attention. However, flowers aren't the only game in town. More and more we are beginning to appreciate the role insects play in the pollination of some gymnosperm lineages. For instance, did you know that many cycad species utilize insects as pollen vectors? The ways in which these charismatic gymnosperms entice insects is absolutely fascinating and well worth understanding in more detail.

Cycads or cycad-like plants were some of the earliest gymnosperm lineages to arise on this planet. They did so long before familiar insects like bees, wasps, and butterflies came onto the scene. It had long been assumed that, like a vast majority of extant gymnosperms, cycads relied on the wind to get pollen from male cones to female cones. Indeed, many species certainly utilize to wind to one degree or another. However, subsequent work on a few cycad genera revealed that wind might not cut it in most cases.

White-haired cycad ( Encephalartos friderici-guilielm i)

White-haired cycad (Encephalartos friderici-guilielmi)

It took placing living cycads into wind tunnels to obtain the first evidence that something strange might be going on with cycad pollination. The small gaps on the female cones were simply too tight for wind-blown pollen to make it to the ovules. Around the same time, researchers began noting the production of volatile odors and heat in cycad cones, providing further incentives for closer examination.

Subsequent research into cycad pollination has really started to pay off. By excluding insects from the cones, researchers have been able to demonstrate that insects are an essential factor in the pollination of many cycad species. What's more, often these relationships appear to be rather species specific.

Cycadophila yunnanensis ,  C. nigra , and other beetles on a cone of  Cycas  sp.

Cycadophila yunnanensis, C. nigra, and other beetles on a cone of Cycas sp.

By far, the bulk of cycad pollination services are being performed by beetles. This makes a lot of sense because, like cycads, beetles evolved long before bees or butterflies. Most of these belong to the superfamily Cucujoidea as well as the true weevils (Curculionidae). In some cases, beetles utilize cycad cones as places to mate and lay eggs. For instance, male and female cones of the South African cycad Encephalartos friderici-guilielmi were found to be quite attractive to at least two beetle genera. 

Beetles and their larvae were found on male cones only after they had opened and pollen was available. Researchers were even able to observe adult beetles emerging from pupae within the cones, suggesting that male cones of E. friderici-guilielmi function as brood sites. Adult beetles carrying pollen were seen leaving the male cones and visiting the female cones. The beetles would crawl all over the fuzzy outer surface of the female cones until they became receptive. At that point, the beetles wriggle inside and deposit pollen. Seed set was significantly lower when beetles were excluded.

Male cone of  Zamia furfuracea  with a mating (lek) assembly of  Rhopalotria mollis  weevils.

Male cone of Zamia furfuracea with a mating (lek) assembly of Rhopalotria mollis weevils.

For the Mexican cycad Zamia furfuracea, weevils also utilize cones as brood sites, however, the female cones go to great lengths to protect themselves from failed reproductive efforts. The adult weevils are attracted to male cones by volatile odors where they pick up pollen. The female cones are thought to also emit similar odors, however, larvae are not able to develop within the female cones. Researchers attribute this to higher levels of toxins found in female cone tissues. This kills off the beetle larvae before they can do too much damage with their feeding. This way, the cycad gets pollinated and potentially harmful herbivores are eliminated. 

Beetles also share the cycad pollination spotlight with another surprising group of insects - thrips. Thrips belong to an ancient order of insects whose origin dates back to the Permian, some 298 million years ago. Because they are plant feeders, thrips are often considered pests. However, for Australian cycads in the genus Macrozamia, they are important pollinators.

Macrozamia macleayi  female cone.

Macrozamia macleayi female cone.

Thrip pollination was studied in detail in at least two Macrozamia species, M. lucida and M. macleayi. It was noted that the male cones of these species are thermogenic, reaching peak temperatures of around   104 °F (40 °C). They also produce volatile compounds like monoterpenes as well as lots of CO2 and water vapor during this time. This spike in male cone activity also coincides with a mass exodus of thrips living within the cones.

Thrips ( Cycadothrips chadwicki ) leaving a thermogenic pollen cone of  Macrozamia lucida.

Thrips (Cycadothrips chadwicki) leaving a thermogenic pollen cone of Macrozamia lucida.

Thrips apparently enjoy cool, dry, and dark places to feed and breed. That is why they love male Macrozamia cones. However, if the thrips were to remain in the male cones only, pollination wouldn't occur. This is where all of that male cone metabolic activity comes in handy. Researchers found that the combination of rising heat and humidity, and the production of monoterpenes aggravated thrips living within the male cones, causing them to leave the cones in search of another home.

Inevitably many of these pollen-covered thrips find themselves on female Macrozamia cones. They crawl inside and find things much more to their liking. It turns out that female Macrozamia cones do not produce heat or volatile compounds. In this way, Macrozamia are insuring pollen transfer between male and female plants.

Thrips up close.

Thrips up close.

Pollination in cycads is a fascinating subject. It is a reminder that flowering plants aren't the only game in town and that insects have been providing such services for eons. Additionally, with cycads facing extinction threats on a global scale, understanding pollination is vital to preserving them into the future. Without reproduction, species will inevitably fail. Many cycads have yet to have their pollinators identified. Some cycad pollinators may even be extinct. Without boots on the ground, we may never know the full story. In truth, we have only begun to scratch the surface of cycads and their pollinators.

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

Further Reading: [1] [2] [3] [4] [5] [6]

Can Plants "Hear" Running Water?

A recently published study suggests that some plants are capable of using sound to locate water. That's right, sound. Although claims of plants liking or disliking certain types of music still belong in the realm of pseudoscience, this research does suggest that plants may be capable of detecting vibrations in an interpretable way. 

To test this idea, Dr. Monica Gagliano of the University of Western Australia germinated pea seeds in specially designed mazes. Each maze looked like an upside-down Y. At the end of each arm, she devised a series of treatments that would force the pea seedlings to "choose" their desired rooting direction. In some treatments she used standing water coupled with water running through a tube. In others she simply played the sounds of running water against the sound of white noise.

The peas were allowed to grow for five days and afterwards were checked to see which direction their roots were growing. Amazingly, the peas seemed to be able to distinguish the sound of actual running water even when there was no moisture gradient present. Peas given the option of sitting or running water in a tube grew their roots towards the tube a majority of the time. Again, this was in the absence of any sort of water gradient in order to eliminate the chances that the peas were simply honing in on humidity.

Interestingly, plants that were played the sound of running water and white noise through speakers seemed to do what they could to avoid the noise. Although the research did not investigate why the peas had an aversion to the recordings, Dr. Gagliano suspects that it might have something to do with the low frequency magnetic currents emitted by the speakers. Previous research has shown that even weak localized magnetic fields are enough to disrupt the structure of developing root cells. 

All of this taken together paints a fascinating picture of plant sensory capabilities. One should take note, however, that the sample sizes used in this experiment were quite small. More, larger experiments will be needed to fully understand these patterns as well as the mechanisms behind them. Still, these findings shed light on cases in which tree roots seem to be so adept at finding sewer pipes, even in the absence of leaks. It also lends to the findings that the roots of trees such as scrub oaks and box elders will often opt for more stable and reliable sources of ground water over the fluctuating uncertainty of nearby stream sources. Finally, there is something to be said that we share as many as 10 of the 50 genes involved in human hearing with plants.

Our understanding of plant sensory capabilities is really starting to blossom (pun intended). Plants aren't the static, sessile organisms so many make them out to be. They are living, breathing organisms fighting for survival. I, for one, am excited for what new discoveries await. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

The World's Only Parasitic Gymnosperm

When we talk about parasitic plants, 99.9% of the time we are talking about angiosperms. However, deep in the mysterious forests of New Caledonia grows the single exception to the rule. Parasitaxus usta is the only parasitic gymnosperm known to exist. The sole member of its genus, P. usta is as strange and beautiful as it is mysterious.

P. usta hails from a strange family of gymnosperms known scientifically as Podocarpaceae. Its purple coloration is absolutely stunning and is the result of high concentrations of anthocyanin pigments in the vacuoles of its cells. Although this strange gymnosperm does in fact produce chloroplasts, they are quite small and the electron transport mechanisms that make photosynthesis possible no longer function.

The true nature of its parasitic lifestyle has remained quite a mystery over the last few decades. A handful of investigations have shown it to be rather unlike any other type of parasitic plant currently known. One of the most bizarre aspects of its morphology is that P. usta does not form any roots. This provided botanists the first clues that it may be a parasite. Further investigation has suggested that, similar to parasitic ericads and orchids, P. usta utilized a fungal intermediary to parasitize the roots of its only known host, another member of the Podocarpaceae family, Falcatifolium taxoides.

Transfer of carbohydrates has been shown to occur through this fungal connection, however, P. usta also seems to obtain nitrogen and water via a direct connection to its host's xylem tissues. In this way it is similar to some mistletoes. As such, it not only can maintain a very high rate of stomatal conductance and a very low water potential, it can also produce cone crops year round. To the best of my knowledge, no other parasitic plant on Earth adopts such a strange combination of strategies.

Despite its unique status, much of the ecology of P. usta remains a complete mystery. For instance, despite being a root parasite, stems of P. usta have been found sprouting from its host tree over 3 feet above the ground. This suggests that P. usta may actually be a strange type of holoparasite. Also, it is entirely unknown how this parasitic gymnosperm becomes established on its host. To date no seed dispersal mechanisms have been described, nor are the seeds sticky. Perhaps its all a matter of chance, which would explain why so few individuals have been found. At the end of the day, the fact that it occurs on a remote island in very few locations means that this bizarrely unique gymnosperm will hold on to its mysteries for many years to come.

Photo Credit: [1] [2]

Further Reading:

http://www.conifers.org/po/Parasitaxus.php

http://bit.ly/2cBUwvj

I've Got the Colorado Blues

Picea_pungens_USDA3.jpg

You would be hard pressed to find a resident of temperate North America who has never seen a Colorado blue spruce. These iconic trees are a staple of every sapling give-away and can be found in countless landscape plans all over the continent. There is no denying the fact that the blue hues of Picea pungens have managed to tap into the human psyche and in doing so has managed to spread far beyond its relatively limited range. However, despite its popularity, few people ever really get to know this species. Even fewer will ever encounter it in the wild. Today I would like to introduce you to a brief natural history of Picea pungens

Despite its common name, P. pungens is not solely a denizen of Colorado. It can be found in narrow swaths of the Rocky Mountains of Wyoming, Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, and of course, central Colorado. There are also some rumored populations in Montana as well. It has a very narrow range compared to its more common relative the Engelmann spruce (Picea engelmannii). Whereas some authors consider the Colorado blue spruce to be a subspecies of the Engelmann spruce, the paucity of natural hybrids where these two species overlap suggests otherwise. It is likely that Colorado blue spruce split off from this lineage and has since followed its own evolutionary trajectory.

Male cones are short-lived but quite attractive.

Male cones are short-lived but quite attractive.

One of the reasons P. pungens has become such a popular landscape tree is due to its extreme hardiness. Indeed, this is one sturdy tree species. Not only can it handle drought, P. pungens is also capable of surviving temperatures as low as -40 degrees Celsius with minimal foliar damage. Little stands in the way of a well established Colorado blue. In the wild it can be found growing on gentle mountain slopes at elevations of 6,000 to 10,000 feet. It is also a long lived and highly fecund tree. The most highly productive seed years for P. pungens begin at age 50 and last until it reaches roughly 150 years of age. Seeds germinate best on bare soils, which probably keeps this species limited to these mountainous areas in the wild.

The typical female cone of the Colorado blue spruce.

The typical female cone of the Colorado blue spruce.

Another component of its landscape popularity is its characteristic blue color. In reality, not all trees exhibit this coloration. Its blue hue is the result of epicuticular wax deposits on the leaves as they are produced in the spring. Not all trees produce the same amount or consistency of wax and therefore not all look blue. Wax production seems to be controlled by a genetic factor and therefore is often a shared trait among isolated populations. The wax functions as sun screen, reflecting harmful UV rays away from sensitive developing foliage. This is why it is most prominent in new growth. The wax can and often does degrade over the span of a growing season, resulting in duller trees come fall. 

Despite how interesting this spruce is, Picea pungens, in my opinion, represents the epitome of lazy landscaping. Like Norway spruce and Norway maples, P. pungens seems to be an all too easy choice for those looking to save a quick buck. As a result, countless numbers of these trees line streets and demarcate property boundaries. Though P. pungens is native to North America, its narrow home range makes its ecological function elsewhere quite minimal. Though one could certainly do worse than planting this conifer, it nonetheless overshadows more ecologically friendly tree choices. 

Photo Credit: [1] [2] [3]

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