Are Crickets Dispersing Seeds of Parasitic Plants?

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Parasitic plants lead a rather unique lifestyle. Many have foregone photosynthesis entirely by living off fungi or their photosynthetic neighbors. Indeed, there are many anatomical and physiological adaptations that are associated with making a living parasitically. Whether they are full parasites or only partial, one thing that many parasitic plants have in common are tiny, dust-like seeds. Their reduced size and thin seed coats are generally associated with wind dispersal, however, there are always exceptions to the rule. Recent evidence has demonstrated that a handful of parasitic plants have evolved in response to a rather unique seed dispersal agent - camel crickets.

A research team based out of Japan recently published a paper describing a rather intriguing seed dispersal situation involving three species of parasitic plants (Yoania amagiensis - Orchidaceae, Monotropastrum humile - Ericaceae, and Phacellanthus tubiflorus - Orobanchaceae). These are all small, achlorophyllous herbs that either parasitize trees directly through their roots or they parasitize the mycorrhizal fungi associated with said trees. What's more, each of these species are largely inhabitants of the dense, shaded understory of rich forests.

These sorts of habitats don't lend well to wind dispersal. The closed forest canopy and dense understory really limits wind flow. It would appear that these three plant species have found away around this issue. Each of these plants invest in surprisingly fleshy fruits for their parasitic lifestyle. Also, their seeds aren't as dusk-like as many of their relatives. They are actually quite fleshy. This is odd considering the thin margins many parasitic plants live on. Any sort of investment in costly tissues must have considerable benefits for the plants if they are to successfully get their genes into the next generation.

Fleshy fruits like this are usually associated with a form of animal dispersal called endozoochory. Anyone that has ever found seed-laden bird poop understands how this process works. Still, simply getting an animal to eat your seeds isn't necesarly enough for successful dispersal. Seeds must survive their trip through the gut and come out the other end relatively in tact for the process to work. That is where a bit of close observation came into play.

After hours of observation, the team found that the usual frugivorous suspects such as birds and small mammals showed little to no interest in the fruits of these parasites. Beetles were observed munching on the fruits a bit but the real attention was given by a group of stumpy-looking nocturnal insects collectively referred to as camel crickets. Again, eating the fruits is but one step in the process of successful seed dispersal. The real question was whether or not the seeds of these parasites survived their time inside either of these insect groups. To answer this question, the team employed feeding trials.

They compared seed viability by offering up fruits to beetles and crickets both in the field and back in the lab. Whereas both groups of insects readily consumed the fruits and seeds, only the crickets appeared to offer the greatest chances of a seed surviving the process. Beetles never pooped out viable seeds. The strong mandibles of the beetles fatally damaged the seeds. This was not the case for the camel crickets. Instead, these nocturnal insects frequently pooped out tens to hundreds of healthy, viable seeds. Considering the distances the crickets can travel as well as their propensity for enjoying similar habitats as the plants, this stacks up to potentially be quite a beneficial interaction. 

The authors are sure to note that these results do not suggest that camel crickets are the sole seed dispersal agents for these plants. Still, the fact that they are effective at moving large amounts of seeds is tantalizing to say the least. Taken together with other evidence such as the fact that the fruits of these plants often give off a fermented odor, which is known to attract camel crickets, the fleshy nature of their fruits and seeds, and the fact that these plants present ripe seed capsules at or near the soil surface suggests that crickets (and potentially other insects) may very well be important factors in the reproductive ecology of these plants.

Coupled with previous evidence of cricket seed dispersal, it would appear that this sort of relationship between plants and crickets is more widespread than we ever imagined. It is interesting to note that relatives of both the plants in this study and the camel crickets occur in both temperate and tropical habitats around the globe. We very well could be overlooking a considerable component of seed dispersal ecology via crickets. Certainly more work is needed.

Photo Credits: [1]

Further Reading: [1] [2]

Resin Midges, Basal Angiosperms, and a Strange Pollination Syndrome

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When we try to talk about clades that are "basal" or "sister" to large taxonomic groups, your average listener either consciously or unconsciously thinks "primitive." Primitive has connotations of something that under-developed or unfinished. This is simply not the case. Take, for instance, a family of basal angiosperms called Schisandraceae.

This family is nestled within the order Austrobaileyales, which, along with a small handful of other families, represent the earliest branches of the angiosperm family tree still alive today.  To call them primitive, however, would be a serious misnomer. Because they diverged so early on, these lineages represent serious success stories in flowering plant evolution, having survived for hundreds of millions of years. Instead, we must think of them as fruitful early experiments in angiosperm evolution.

Floral morphology of and interaction between midge and their larvae (white arrows) in Illicium dunnianum

Still, the proverbial proof is in the pudding and if there was any sort of physical evidence one could put forth to remove our hierarchical prejudices about the taxonomic position of these plants, it would have to be their bizarrely specific pollination syndromes.  Members of the family Schisandraceae have entered into intense relationships with a group of flies known as midges and their interactions are anything but primitive. 

We will start with two species of plant native throughout parts of Asia. Meet as Illicium dunnianum and Illicium tsangii. More will be familiar with this genus than they may realize as Illicium gives us the dreaded star anise flavor our grandparents liked to sneak into our cookies as kids (but I digress). These particular species, however, have more to offer the world than flavoring. They are also very important plants for a group of gall midges in the genus Clinodiplosis.

The midges cannot reproduce without I. dunnianum or I. tsangii. You see, these midges lay their eggs within the flowers of these plants and, in doing so, end up pollinating them in the process. At first glance it may seem like a very one-sided relationship. Female midges deposit their eggs all along the carpels packed away inside large, fleshy whorl of tepals. As the midges crawl all over the reproductive organs looking for a suitable place to lay, they inevitably pick up and deposit pollen. 

Floral morphology and interaction between midge larvae (white arrows) in  Illicium tsangii

This is not the end of this relationship though. After eggs have been deposited, something strange happens to the Illicium flowers. For starters, they develop nursery chambers around the midge larvae. Additionally, their tepals begin producing heat. Enough heat is produced to keep the nursery chamber temperature significantly warmer than the ambient air temperature. What's more flower heating intensifies throughout the duration of fruit development. It was originally hypothesized that this heating had something to do with floral odor volatilization and seed incubation, however, experiments have shown that at least seed development in these two shrubs is not influenced by floral heat in any major way. The same cannot be said for the midge larvae. 

As the flowers mature and give way to developing seeds, the midge larvae are hard at work feeding on tiny bits of the flowers themselves. When researchers looked at midge larvae development on these Illicium species, they found that they were completely dependent upon the floral heat for survival. Any significant drop in temperature caused them to die. Essentially, the plants appear to be producing heat more for the midges than for themselves. It may seem odd that these two plants would invest so much energy to heat their flowers so that midge larvae feeding on their tissues can survive but such face-value opinions rarely stand in ecology.

One must not forget that those larvae grow up to be adult midges that will go on to pollinate the Illicium flowers the following season. Although the plants are taking a bit of a hit by allowing the larvae to develop within their tissues, they are nonetheless ensuring that enough pollinators will be around to repeat the process again. If that wasn't cool enough, the relationship between each of these plants and their pollinators are rather specific and the authors of at least one paper believe that the midges that pollinate each species are new to science. 

Now, if I haven't managed to convince you that this angiosperm sister lineage is anything but primitive, then let's take a look at another genus within the family Schisandraceae that have taken this midge pollination syndrome to the next level. This story also takes place in Asia but instead involves a genus of woody vines known as Kadsura

Like the Illicium we mentioned earlier, a handful of Kadsura species rely on midges for pollination. The way in which they go about maintaining this relationship is a bit more involved. The midges that are attracted by Kadsura flowers are known as resin midges and their larvae live off of plant resins. The flowers of Kadsura are another story entirely. They are as odd as they are beautiful. 

Flowers, pollinators ,and their larvae (white arrows) in Kadsura heteroclita.

Flowers, pollinators ,and their larvae (white arrows) in Kadsura heteroclita.

In male flowers, stamens are arranged in dense, cone-like structures called androecia whereas the female flowers contain a compact shield-like structure with the uppermost part of the stigma barely emerging. This is called a gynoecium. Even weirder, the male flowers of one particularly strange species, Kadsura coccinea, produce large, swollen inner tepals. 

Once Kadsura flowers begin to open, visiting midges are not far behind. Male flowers seem to attract more midges than female flowers and it is thought that this has to do with varying amounts of special attractant chemicals produced by the flowers themselves. Regardless, midges set to work exploring the blooms with males looking for mates and females looking for a place to lay their eggs. 

When a suitable spot has been found, females will deposit their eggs into the floral tissues with their ovipositor. The wounded plant tissues immediately begin producing resin, not unlike a wounded pine tree. In the case of K. coccinea, it would appear that the oddly swollen tepals are specifically targeted by female midges for egg laying. They too produce resin upon having eggs laid within. 

The oddball flowers of Kadsura coccinea showing swollen tepals.

The function of plant resins in many cases are to fight off pathogens. From beetles to fungi, resin helps plug up and seal off wounds. This does not seem to be the case in the Kadsura-midge relationship though. The so-called "brood chambers" within the floral tissues go on producing resin for upwards of 6 days after the midge eggs were laid. Eventually the floral parts whither and drop off but the midge larvae seem to be quite happy in their resin-filled homes. 

As it turns out, the resin midge larvae feed on the viscous resin as their sole food source. Instead of trying to ward off these pesky little insects, the plants seem to be encouraging them to raise their offspring within! Just as we saw in the Asian Illicium, these Kadsura vines seem to be providing brood sites for their pollinators. Also, just as the Illicium-midge relationship thought to be species specific, each species of Kadsura appears to have its own specific species of resin midge pollinator! K. coccinea even goes as far as to produce tepals specifically geared towards raising midge larvae, thus keeping them away from their more valuable reproductive organs. In return for the nursery service, Kadsura have their pollinators all to themselves.

Pollination mutualisms in which plants trade raising larvae for pollen transfer are extremely derived and some of the most specialize plant/animal interactions on the planet. To find such relationships in these basal or sister lineages is living proof that these plants are anything but primitive. In the energy-reproductive investment trade-off, it appears that ensuring ample pollinator opportunities far outweighs the cost of providing them with nursery chambers. It is remarkable to think just how intertwined the relationships between these plants and there pollinators truly are. Take that, plant taxonomic prejudices! 

Photo Credits: [1] [2]

Further Reading: [1] [2] 

 

A Truly Bizarre Cactus From The Amazon

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When we think of cacti, we tend to think of dry deserts and sandy soils. Few of us would ever jump to the trunk of a tree, nestled in a humid rainforest, and experiencing periodic inundation. Yet, such a habitat is the hallmark of one of the world's most unique species of cactus - Selenicereus witii. In more ways than one, this species is truly aberrant.

Whereas epiphytic cacti aren't novel, the habits of S. witii surely push the limits of what we know about the entire cactus family. Despite having been discovered in 1899, little attention has been paid to this epiphytic cactus. What we do know comes from scant herbarium records and careful observation by a small handful of botanists.

S. witii is endemic to a region of central Amazonia and only grows in Igapó, or seasonally flooded, blackwater forests. It makes its living on the trunks of trees and its entire morphology seems particularly adapted to such a harsh lifestyle. Unlike most cacti, S. witii doesn't seem to bother with water storage. Instead, its stems grow completely appressed to the trunks of trees. Roots emerge from near the spine-bearing areoles and these help to anchor it in place. 

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Because they are often exposed to bright sunlight, the stems produce high amounts of chemical pigments called betalains. These act as sun block, protecting the sensitive photosynthetic machinery from too much radiation. These pigments also give the plant a deep red or purple color that really stands out against the trunks of trees. 

Like all members of this genus, S. witii produces absolutely stunning flowers. However, to see them, your best bet is to venture out at night. Flowers usually begin to open just after sundown and will be closed by morning. And my, what flowers they are! Individual blooms can be upwards of 27 cm long and 12.5 cm wide (10 in by 5 in)! They are also said to produce an intense fragrance. Much of their incredible length is a nectar tube that seems to be catered to a specific group of sphinx moths, whose proboscis is long enough to reach the nectar at the bottom.

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The seeds of S. witii are just as aberrant as the rest of the cactus. They are rather large and shaped like a kidney. Cross sections reveal that most of their size is devoted to hollow air chambers. Indeed, the seeds float like tiny pieces of cork when placed in water. This is likely an adaptation resulting from their preferred habitat.

As mentioned above, S. witii has only been found growing in seasonally flooded forests. What's more, plants only occur on the trunks of large trees right at the high water line. In fact, the highly appressed nature of its stems seems to suggest that this species can withstand periodic submergence in fast flowing water. The seeds must also cope with flooding and it is likely that their buoyant nature aids in seed dispersal during these periods. 

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All in all, this is one weird cactus. Although it isn't alone in its tropical epiphytic habit, it certainly takes the cake for being one of the most derived. Aside from a few publications, little attention has been given to this oddball. It would appear that the seasonal flooding of its preferred habitat has simply chased this cactus up into the trees, the environmental demands of which coaxed out strange but ingenious adaptations from its genome. The good news is that where it does occur, S. witii seems to grow in high numbers.

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

Further Reading: [1]

Devil's Gardens

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Imagine, if you will, walking through the dense understory somewhere in the Amazon basin. Diversity reigns supreme here and it would seem that every few steps reveals myriad new plant species. As you walk along, something in the vegetation changes. You stumble into a clearing in the middle of the forest dominated entirely by a single species of tree. Why the sudden change? How did this monoculture develop? You, my friend, have just found yourself on the edge of a Devil's garden. 

Devil's gardens are said to be the resting place of an evil spirit known to local tribes as Chullachaki. Anyone unlucky enough to stumble into his garden is said at risk of attack or curse. In reality, these gardens have a biological origin. The real gardeners are a handful of ant species which seem to have rather specific gardening preferences. Careful inspection would reveal that the gardens largely consist of trees in one of three genera - Duroia, Tococa, or Clidemia

Tococa sp. (Melastomataceae)

Tococa sp. (Melastomataceae)

The reason that ants are so fond of these genera has to do with housing. These plant groups contain species which produce swellings along their stems and petioles known as domatia. These domatia are hollow and are the favorite nesting spots of various ant species. Ant colonies set up shop within. As anyone who has ever blundered into an ant colony can attest, ants are quite voracious at defending their home. 

By providing ant colonies with a home base, these plants have essentially hired body guards. It is a wonderful form of symbiosis in which the ants aggressively defend against anything that might want to take a bite out of their host tree. Any herbivore trying to take up residence or lay eggs within the Devil's garden is viciously attacked. In doing so, the ants are protecting their host trees at the cost of all other plants unlucky enough to germinate within the garden. Still, this anti-herbivore behavior doesn't totally explain the monoculture status these host trees achieve within the garden itself. Why are these gardens so ominously devoid of other plant species?

To answer this, one would have to watch how the ants behave as they forage. While scouting, if ants encounter a seedling of their host tree, nothing really happens. They go about their business and let the seedling grow into a future home. When they encounter a non-host tree, however, their behavior completely changes. 

Behold - A Devil's Garden

Behold - A Devil's Garden

The ants begin biting the stem of the plant, exposing its vascular tissue. As they bite, the ants also sting the foreign seedling, injecting minute amounts of formic acid into the wound. One or two ants isn't enough to bring down a seedling but one thing ants have on their side are numbers. Soon an entire platoon of ants descend upon the hapless seedling, stinging it repeatedly. In no time at all, the seedling succumbs to the formic acid injections and dies. By repeating this process any time a foreign plant is found growing within the vicinity of the garden, the resident ants ensure that only trees that will produce domatia are allowed to grow in their garden. Thus, a Devil's garden has been formed. 

Although this relationship seems incredibly beneficial for each party, it does come at some cost to the plants themselves. Certainly forming the domatia is a costly endeavor on the part of the plant, but research has also shown that growing in such high, monoculture-like densities in the jungle has its downsides. It has been found that individual host trees can actually experience more herbivore pressures when growing within a Devil's garden than if it was growing alone, elsewhere in the forest. 

Despite their aggression towards herbivores, the ants simply cannot be everywhere at once. As such, the high densities of host tree species within a Devil's garden act like a dinner bell for any insect that enjoys feeding on that particular type of plant. Essentially, the ants are concentrating a potential food source. Experts believe that this might explain why Devil's gardens never completely take over entire swaths of forest. Essentially, there are diminishing returns to living in such high densities. Still, benefits must outweigh costs if such mutualisms are to be maintained and it is quite obvious that both plant and ant benefit from this interaction to a great degree. 

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

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

The Elusive White Walnut

Today we go in search of the elusive white walnut (Juglans cinerea). Many of you may know it by its other common name - the butternut. Sadly, being able to find large, mature specimens of this wonderful tree is getting harder and harder. Watch and find out why...

 

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The Early Days Of A Symbiosis?

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Despite the ubiquitous nature of symbioses across the globe, evidence of their origins is scant to say the least. Mostly we look for clues of their origin hidden within the fossil record. Excitingly, a series of fossils discovered in Scotland reveal what very well be the early days of plant-cyanobacterial interactions. Thanks to these exquisitely preserved fossils, we now have the earliest record of an association between these two groups of organisms.

The fossils themselves date back to the early Devonian, some 400 million years ago. They hail from a hot spring community which allowed wonderfully detailed preservation of everything down to the cellular level. Needless to say, this was a drastically different time for life on this planet. Plants were really starting to dominate the landscape. In the case of the fossil discoveries in question, one plant in particular is the star of this show. 

Meet Aglaophyton major. This odd looking plant would have been a common site in these sorts of habitats. It largely consisted of a small, leafless stem that branched as it ambled over the ground. These stems bore the stomata, which allowed gas exchange to occur. Every once in a while, a stem would throw up a reproductive structure called a sporangium, which housed the spores. At the ground level, the stems would occasionally produce root-like rhizoids that have been found in association with fossilized mycorrhizal fungi in the soil.

In total, A. major only stood about 18 cm in height. Though abundant, it was relatively small compared to some of the other vegetation coming online at this point in time. It is likely that A. major could tolerate occasional flooding. In fact, some have speculated that flooding may have been necessary for the germination of its spores. It's this periodic inundation with water that likely led to an interesting and tantalizing relationship with cyanobacteria. 

1. Transverse section through two typical axes showing the simple internal organization; slide P1828; bar = 1 mm. 2. Anatomy of the prostrate mycorrhizal axis (E = epidermis; OC = outer cortex; MAZ = mycorrhizal arbuscule-zone; IC = inner cortex; PIT = phloem-like tissue; CT = conducting tissue); slide P1612; bar = 150 μm. 3. Dense aggregate of cyanobacterial filaments in an area where the axis is injured and has exuded some type of wound secretion (opaque mass); slide P1289; bar = 100 μm. 4. Detail of Plate I, 3, showing part of the cyanobacterial aggregate; bar = 100 μm. 5. Intercellular cyanobacterial filaments near the mycorrhizal arbuscule-zone of the cortex (darker tissue in lower third of image); slide P3652; bar = 50 μm. 6. Group of filaments passing through the intercellular system of the outer cortex; slide P3652; bar = 20 μm.

1. Transverse section through two typical axes showing the simple internal organization; slide P1828; bar = 1 mm. 2. Anatomy of the prostrate mycorrhizal axis (E = epidermis; OC = outer cortex; MAZ = mycorrhizal arbuscule-zone; IC = inner cortex; PIT = phloem-like tissue; CT = conducting tissue); slide P1612; bar = 150 μm. 3. Dense aggregate of cyanobacterial filaments in an area where the axis is injured and has exuded some type of wound secretion (opaque mass); slide P1289; bar = 100 μm. 4. Detail of Plate I, 3, showing part of the cyanobacterial aggregate; bar = 100 μm. 5. Intercellular cyanobacterial filaments near the mycorrhizal arbuscule-zone of the cortex (darker tissue in lower third of image); slide P3652; bar = 50 μm. 6. Group of filaments passing through the intercellular system of the outer cortex; slide P3652; bar = 20 μm.

Cyanobacteria are probably best known for their contribution of oxygen to Earth's early atmosphere. What's more, many also fix nitrogen. That is why the fossil discovery of A. major with cyanobacteria in and around its cells is so exciting. These 400 million year old fossils provide the first evidence of a plant and cyanobacteria in an intimate association.

As mentioned above, the fossilization process was so thorough that it preserved subcellular structures. After thin sectioning some A. major stems, a team of researchers found filaments of cyanobacteria in the process of invading the plant and taking up residence. The cyanobacteria appears to be entering the plant through the stomatal openings along the stem. Once inside, the cyanobacteria show signs of colonazation of substomatal chambers as well as intercellular spaces within the plants tissues.

Although the authors cannot say whether this association was mutualistic or not, it nonetheless represents a model situation detailing how such a symbiotic relationship could have evolved in the first place. Because the cyanobacteria in question here is thought to be aquatic, the only way for it to move into the plant would have been during periodic flooding events. The idea that this could be simply an infection following the death of the plant was considered. However, the non-random distribution of cyanobacteria within A. major cells suggests that this relationship was no accident.

For now, the relationship between A. major and cyanobacteria was likely an "on-again–off-again incidental association" centered around flood events. The fact that A. major was already associated with mycorrhizal fungi at this point in Earth's history certainly suggests that the genetic adaptations necessary for symbiotic relationships were already in place. Though it isn't a smoking gun, these fossils provide the earliest evidence of plants' relationship with cyanobacteria.

Photo Credits: [1]

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

A Common Plant With An Odd Pollination Mechanism

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Pollination is not an altruistic enterprise. Each party involved is trying to maximize its gains while minimizing its losses. Needless to say, cheaters abound in natural systems. As such, plants have gone to great lengths to ensure that their reproductive investments pay off in the long run. Take, for instance, the case of the fragrant water-lily (Nymphaea odorata). 

Most of us have encountered this species at some point in our lives. Those who have often remark on the splendor of their floral displays. Certainly this is not lost on pollinators either. Coupled with their aromatic scent, these aquatic plants must surely be a boon to any insect looking for pollen and nectar. Still, the flowers of the fragrant water-lily take no chances.

Close observation will reveal an interesting pattern in the blooming cycle of this water-lily. On the first day that the flowers open, only the female portions are mature. The structure itself is bowl-like in shape. Filling this stigmatic bowl is a viscous liquid. After the first day, the flowers close for the evening and reopen to reveal that the stigma is no longer receptive and instead, the anthers have matured.

Many insects will visit these floating flowers throughout the blooming period. Everything from flies, to beetles, and various sorts of bees have been recorded. Seed set in this species is pollen limited so any insect visiting a female flower must deposit pollen if reproduction is to be achieved. This is where that bowl of sticky liquid comes into play. The liquid itself is rather unassuming until you see an insect fall in.

Due to the presence of surfactants, any insect that falls into the fluid immediately sinks to the bottom. The flowers seem primed to encourage this to happen too. The flexible inner stamens that surround the bowl bend under the weight of heavier insects, thus dumping them into the liquid below. Only by observing this process under extreme magnification does all of this make sense.

The liquid within the bowl essentially washes off any pollen that a visiting insect had stuck to its body. As the pollen falls off, it drifts down to the bottom of the bowl where it contacts the receptive stigma. Thus, cross-pollination is achieved. Most of the time, insect visitors are able to crawl out without any issue. However, the occasional insect will drown within the fluid. Alas, that is no sweat off the water-lily's back. Having dropped off the pollen it was carrying, it is of little use to that flower anymore.

Once a water-lily flower has been fertilized, its stem begins to curl up like a spring. This draws the ovaries underwater where they can develop in relative safety. It also ensures that, upon maturing, the seeds are more likely to find a suitable underwater site for germination. To think that this drama plays out time and time again unbeknownst to the casual observer is something I find endlessly fascinating about the natural world.

Photo Credit: [1] [2]

Further Reading: [1] [2]

The First Trees Ripped Themselves Apart To Grow

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A new set of fossil discoveries show that the evolutionary arms race that are forests started with plants that literally had to rip themselves apart in their battle for the canopy. The first forests on this planet arose some 385 million years ago and were unlike anything we know today. They consisted of a clade of trees known scientifically as Cladoxylopsids, which have no living representatives in these modern times. How these trees lived and grew has remained a mystery since their fossilized trunks were first discovered but a new set of fossils from China reveals that these trees were unique in more ways than one.

Laying eyes on a full grown Cladoxylopsid would be a strange experience to say the least. Their oddly swollen base would gradually taper up a trunk that stretched some 10 to 12 meters (~30 - 40 feet) into a canopy of its relatives. They had no leaves either. Instead, their photosynthetic organs consisted of branch-like growths that were covered in twig-like projections. Whereas most fossils revealed great detail about their outward appearance, we have largely been in the dark on what their internal anatomy was like. Excitingly, a set of exquisitely preserved fossils from Xinjiang, China has changed that. What they reveal about these early trees is quite remarkable.

As it turns out, the trunks of these early trees were hollow. Unlike the trees we know today, whose xylem expands in concentric rings and forms a solid trunk, the trunk of Cladoxylopsid was made up of strands of xylem connected by a network of softer tissues. Each of these strands was like a mini tree in and of itself. Each strand formed its own concentric rings that gradually increased the size of the trunk. However, this gradual expansion did not appear to be a gentle process.

As these strands increased in size, the trunk would grow larger and larger. In doing so, the tissues connecting the strands were pulled tighter and tighter. Eventually they would tear under the strain. They would gradually repair themselves over time but the effect on the trunk was quite remarkable. In effect, the base of the tree would literally collapse in on itself in a controlled manner. You could say that older Cladoxylopsids developed a bit of a muffin top at their base. 

A cross section of a Cladoxylopsid trunk showing the hollow center, individual xylem strands, and the network of connective tissues.

A cross section of a Cladoxylopsid trunk showing the hollow center, individual xylem strands, and the network of connective tissues.

Although this seems quite detrimental, the overall structure of the tree would have been quite sturdy. The authors liken this to the design of the Eiffel tower. Indeed, a hollow cylinder is actually stronger than a solid one of the same dimensions. When looked at in the context of all other trees, this form of growth is pretty unique. No other trees are constructed in such a manner.

The authors speculate that this form of growth may be why these trees eventually went extinct. It would have taken a lot of energy to grow in that manner. It is possible that, as more efficient forms of growth were evolving, the Cladoxylopsids may not have been able to compete. It is anyone's guess at this point but this certainly offers a window back into the early days of tree growth. It also shows that there has always been more than one way to grow a tree.

Photo Credits: [1] [2]

Further Reading: [1]

Bird Pollination Of The Bird Of Paradise

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Who hasn't stared in wonderment at the inflorescence of a bird of paradise? One doesn't need too much of an imagination to understand how these plants got this common name. Flowers, however, did not evolve in response to our aesthetic tastes. They are solely for sex and in the case of bird of paradise, Strelitzia reginae, pollination involves birds.

In its native range in South Africa, S. reginae is pollinated by sunbirds, primarily the Cape weaver (Ploceus capensis). That alluring floral morphology is wonderfully adapted to maximize the chances of successful cross-pollination by their avian visitors. Cape weavers are looking for a sip of energy rich nectar. To get at said nectar, the birds must perch on the inflorescence. Not any position will do either.

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To get their reward, the birds must perch so that their beaks are at just the right angle to reach down into the floral tubes. The plant ensures this by providing a convenient perch. Those fused blue petals are structurally reinforced and actually serve as a convenient perch! Upon alighting on the perch, the hidden anthers are thrust outward from their resting chamber, brushing up against the bird's feet in the process. The Cape weaver doesn't move around much once on the flower so self pollination is minimized.

When the bird visits another plant, the process is repeated and pollination is achieved. Seed set is severely pollen limited. This is a good thing considering how popular they are in cultivation. Plants growing outside of South Africa rarely set seed without a helping hand. However, here in North America, some birds seemed to have figured out how to get at bird of paradise nectar.

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Observations made in southern California found that at least one species of warbler, the common yellowthroat (Geothlypis trichas), not only made regular visits to a stand of S. reginae, it also seemed to figure out the proper way to do so. Individuals were seen perching on the floral perch and drinking the nectar. They were pretty effective visitors at that. Of the 14,400 inflorescence found within the study area, 88% of them produced viable seed! It seems that far from its native range, S. reginae has a friend in at least one New World warbler. Armed with this knowledge, land owners should be vigilant to ensure this plant doesn't become a problem in climates suitable for its growth.

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

Further Reading: [1]

 

Appalachia

Welcome to Appalachia. I have fallen in love with this corner of the world in large part because of its wonderfully rich and unique flora. Join In Defense of Plants as we take a sneak peak at a mere fraction of the botanical riches these mountains hold.

Further Readings On Appalachian Flora:

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Producer, Writer, Creator, Host: Matt Candeias

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Of Acorns and Squirrels

I find it fun to watch squirrels frantically scurrying about during the fall. Their usually playful demeanor seems to have been replaced with more serious and directed undertones. If you watch squirrels close enough you may quickly realize that, when it comes to oaks, squirrels seem to have a knack for taxonomy. They quickly bury red oak acorns while immediately set to work on eating white oak acorns. Why is this?

Music by:
Artist: Botanist
Track: Stargazer
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A Bat-Pollinated Passion Flower From Ecuador

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Say "hello" to one of Passiflora's most recent additions, the bat-pollinated Passiflora unipetala. The first specimens of this vine were discovered back in 2009 by Nathan Muchhala while studying flower visiting bats in northern Ecuador. It is a peculiar member of the genus to say the least. 

One of the most remarkable features of this plant are its flowers. Unlike its multi-petaled cousins, this species stands out in producing a single large petal, which is unique for not only the genus, but the whole family as well. The petal is quite large and resembles a bright yellow roof covering the anthers and stigma. At the base of the flower sits the nectar chamber. The body of the plant consists of a vine that has been observed to grow upwards of 6 meters up into the canopy.

Flowering in this species occurs at night. Their large size, irregular funnel shape, and bright yellow coloring all point to a pollination syndrome with bats. Indeed, pollen of this species has been found on the fur of at least three different bat species. Multiple observations (pictured here) of bats visiting the flowers helped to confirm. Oddly enough for a bat-pollinated plant, the flowers produce no detectable odor whatsoever. However, another aspect of its unique floral morphology is worth noting. 

The surface of the flower has an undulating appearance. Also, the sepals themselves have lots of folds and indentations, including lots of dish-shaped pockets. It is thought that these might help the flower support the weight of visiting bats. They may also have special acoustic properties that help the bats locate the flowers via echolocation. Though this must be tested before we can say for sure, other plants have converged on a similar strategy (read here and here).

As it stands currently, Passiflora unipetala is endemic to only a couple high elevation cloud forests in northern Ecuador. It has only ever been found at two locations and sadly a landslide wiped out the type specimen from which the species description was made. As such, its introduction to the world came complete with a spot on the IUCN Redlist as critically endangered. Luckily, the two localities in which this species has been found are located on privately protected properties. Let's just hope more populations are discovered in the not-too-distant future.

Photo Credits: [1] 

Further Reading: [1]

Ants As Pollinators?

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Ants interact with plants in a variety of beneficial ways. They offer protection, they provide nutrients, they even disperse seeds! When it comes to pollination, however, plants have largely gone elsewhere. That's not to say ants don't get directly involved in the sex lives of plants. At least one plant species native to Spain has been found to be pollinated by ants. Certainly there are probably more examples of ant pollination throughout the plant kingdom, we simply have to look. For example, one possible ant-pollinated plant can be found growing on the west coast of North America.

The dwarf owl's-clover (Triphysaria pusilla) is a small annual member of the broomrape family. It really is a dwarf species, rarely exceeding a few inches in height. What it lacks in size, it makes up for in abundance. Large colonies of these species can be found growing among other low statured herbs in wetter areas like spring-fed grasslands. Their tendency to produce lots of anthocyanin pigments in their tissues means that these maroon colonies really stand out. Like other members of the family, it is a facultative hemiparasite, tapping into the roots of surrounding vegetation with its roots, stealing nutrients and water as the situation demands.

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Flowering in the dwarf owl's-clover is rather inconspicuous. The dense flowering spikes produce minute, tubular, maroon-yellow flowers. It has been observed that, at any given point during the flowering season, only three flowers will have matured on any given plant. Two of these flowers mature their anthers first whereas the remaining flower matures its stigma. This is likely an adaptation for increasing the chances of cross pollination. 

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Because these flowers hardly qualify as an attractive display for more commonly encountered insect pollinators, it has been hypothesized that ants are the preferred pollinator of this species. Early work even suggested that the dense leaf arrangement facilitates ant movement to and from flowers in any given colony. Although no one has yet quantified the efficacy of ants as pollinators of this species, numerous observations of ants visiting flowers and picking up pollen have been made. Famously, such a scene was filmed for the 1981 documentary "Sexual Encounters of the Floral Kind."

Whether these visits constitute effective pollination remains to be seen. It could be that the ants are nothing more than nectar and pollen thieves. What's more, many ants produce substances from specialized glands that, among other things, destroy pollen. Until someone takes the time to study this interaction, we simply do not know. Sounds like a fun research project to me! 

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

Further Reading: [1]

The Nitrogen-Fixing Abilities of Cycads

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Long before the first legumes came onto the scene, the early ancestors of Cycads were hard at work fixing atmospheric nitrogen. However, they don't do this on their own. Despite being plentiful in Earth's atmosphere, gaseous nitrogen is not readily available to most forms of life. Only a special subset of organisms are capable of turning gaseous nitrogen into forms usable for life. Some of the first organisms to do this were the cyanobacteria, which has led them down the path towards symbioses with various plants on many occasions. 

Cycads are but one branch of the gymnosperm tree. Their lineage arose at some point between the Carboniferous and Permian eras. Throughout their history it would seem that Cycads have done quite well in poor soils. They owe this success to a partnership they struck up with cyanobacteria. Although it is impossible to say when exactly this happened, all extant cycads we know of today maintain this symbiotic relationship with these tiny prokaryotic organisms. 

Cross section of a coralloid cycad root showing the green cyanobacteria inside.

Cross section of a coralloid cycad root showing the green cyanobacteria inside.

The relationship takes place in Cycad roots. Cycads don't germinate with cyanobacteria in tow. They must acquire them from their immediate environment. To do so, they begin forming specialized structures called precoralloid roots. Unlike other roots that generally grow downwards, these roots grow upwards. They must situate themselves in the upper layer of soil where enough light penetrates for cyanobacteria to photosynthesize.

The cyanobacteria enter into the precoralloid roots through tiny cracks and take up residence. This causes a change in root development. The Cycad then initiates their development into true coralloid roots, which will house the cyanobacteria from that point on. Cycads appear to be in full control of the relationship, dolling out carbohydrates in return for nitrogen depending on the demands of their environment. Coralloid roots can shed and reform throughout the lifetime of the plant. It is quite remarkable to think about how nitrogen-fixing symbiotic relationships between plants and microbes have evolved independently throughout the history of life on this planet.

Photo Credits: [1] [2]

Further Reading: [1] [2]

 

The Hidden Anatomy of Grass Flowers

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Grass flowers have their own unique beauty. Examine them with a hand lens and a whole new world of angiosperm diversity suddenly opens up. Unlike other flowering plants, their charm lies not in showy sepals or petals, but in an intricacy centered around the utilization of wind for pollination. However, such floral organs are not lacking. Grass flowers do in fact produce a perianth, the function of which has been highly modified.

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To see what I am referring to, you need to do some dissection under a scope. Pull off a flower and peel away the sheaths (the palea and lemma) that cover it. Inside you will see an ovary complete with feathery stigmas as well as the anthers. At the base of the ovary sits a pair of scales called lodicules. These lodicules are thought to be the rudimentary remains of the perianth. They certainly don't resemble sepals or petals but that is because the function of these structures is not to attract pollinators. They assist in pollination in another way.

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When grass flowers are ready for reproduction, the lodicules begin to swell. This swelling serves to push apart the rigid palea and lemma that protected the flowering parts as they developed. Once apart, the anthers and stigma are free to emerge and let wind do the dirty work for them. Lodicules differ quite a bit from species to species in their size, shape, and overall appearance. Much of this is likely tied to the overall structure in grass flowers.

Photo Credits: [1] [2]

Further Reading: [1]

 

Juicy Citrus

I was enjoying some citrus the other day when I got to thinking about these peculiar fruits. They are some of my favorites yet I know very little about their development. What is a citrus fruit exactly and why are they so juicy?

To start with, citrus fruits are produced by members of the citrus or rue family - Rutaceae. Not all members of this family produce them either. Technically speaking, the oranges, lemons, limes (etc.) we eat are specialized berries called "hesperidia." They are characterized by their tough rind and juicy interior.

Following fertilization, the ovary of each flower begins to swell. The rind is referred to as the pericarp. The pericarp itself has a few layers associated with it but this is where the oil-filled pits are located. Anyone that has ever squeezed an orange peel has seen these pits spurt their contents.

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Inward from the pericarp are a series of segments, which are the carpels. The individual carpels are the reason why oranges can be so easily segmented. Inside each carpel is a locule. These are small cavities where the seeds are housed. Lining the walls of these loculi are tiny hairs that, as the fruit matures, gradually fill with juices.

These juice-filled hairs makeup the pulp of a citrus fruit. Look closely and you can see that they are indeed individual compartments. This not only provides some nutrients to the developing seeds, it also provides a meal for potential seed dispersers, thus increasing the chances of successful recruitment away from the parent tree.

From a quick snack I spiraled into a world of new information. It is amazing what you can learn from simple questions. As a botanically oriented person, every meal offers a sea of discovery!

Photo Credit: [1] [2]

Further Reading: [1]

Arctic Foxes: The Unintentional Gardeners

Predators are an integral component of any healthy ecosystem. Their influence can even be felt at the botanical level via what are called top-down controls. Either through direct predation or through altering their behavior, predators influence the herbivores in any system, which usually results in healthier plant communities. This method is rather indirect but new evidence shows that in the Arctic tundra, a top predator is having quite a direct influence on plant communities.

What's not to love about Arctic foxes? All anthropomorphic views aside, Arctic foxes are important predators in this ecosystem. Although the food web complexity on the tundra is largely driven by limits to plant productivity, a paper published in 2016 shows that these little canids can have profound effects on vegetation. This doesn't have to do with predation directly but rather their reproductive behavior. 

Arctic foxes live, give birth, and raise their young in underground dens. Without these subterranean homes, the foxes would be much more vulnerable to other predators as well as the harsh Arctic climate. Dens don't happen overnight either. Suitable sites are tended for generations and some dens may well be more than a century old. All this equates to a lot of activity in and around a good den site. 

With an average litter size of 8 - 10 pups per female, one can imagine the food and waste buildup must be considerable. Like all predators, Arctic fox food and waste are rich in nitrogen and phosphorus compounds, the necessary building blocks of life. Many an onlooker has noticed that, unsurprisingly, plant growth around Arctic fox dens is much more lush than on the surrounding landscape. Until recently though, such differences have hardly been quantified.

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By examining the soil and plant characteristics around Artic fox dens in Canada and comparing these data to surrounding sites without Arctic fox dens, a team of researchers put the first comprehensive numbers to the effects of Arctic foxes on tundra plant communities. They found that soils from in and around Arctic fox dens contained significantly higher levels of nitrogen and phosphorus than did the surrounding control plots. What's more, these levels varied throughout the year. In June, for instance, soil nitrogen and phosphorus levels were 71% and 1195% higher than non-den soils. These levels seemed to switch later in the summer. In August, soil nitrogen from fox dens were 242% higher and soil phosphorus levels were 191% higher.

As you can probably imagine, all of these extra nutrients caused a change in vegetation around the dens. Den sites were far more productive in terms of vegetation. The team found that, on average, Arctic fox dens supported 2.8 times more plant biomass than did the surrounding area. The authors note that these were conservative estimates and that the true values are much higher. Taken together, these results demonstrate that far from simply being top predators, Arctic foxes are true ecosystem engineers, at least on local scales. This is especially important in such a demanding ecosystem as the Arctic tundra.

Photo Credits: [1] [2]

Further Reading: [1]

Meet the Sweetfern

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I remember the first time I laid my eyes on Comptonia peregrina. I was new to botany at that point in my life so I didn't have a well developed search image for these sorts of things. I was scrambling down a dry ridge with a scattered overstory of gnarly looking chestnut oaks when I saw a streak of green just below me on a sandy outcropping. They were odd looking plants, the likes of which I had never seen before.

I took out my binoculars to get a better look. What were these strange organisms? Were they ferns? No, they seemed to have woody stems. Were they gymnosperms? No, I could make out what appeared to be male catkins. Luckily I never leave home without a field guide or two. Using what little terminology I knew, I was able to narrow my focus to a plant commonly called a "sweetfern."

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This was one of the first instances in which I grasped just how troublesome common names can be. C. peregrina is mostly definitely not a fern. It is actually an angiosperm that hails from the bay family (Myricaceae). Comptonia is a monotypic genus, with C. peregrina being the only species. It is a denizen of dry, nutrient poor habitats. As such, it has some wonderful adaptations to deal with these conditions.

To start with, its a nitrogen fixer. Similar to legumes, it forms nodules on its roots that house specialized nitrogen-fixing bacteria called rhizobia. This partnership takes care of its nitrogen needs, but what about others? One study found that not only do the roots form nodules, they also form dense cluster roots. Oddly, closer observation found that these clusters were not associated with mycorrhizal fungi. What's more, they also found that these structures were most prevalent in highly disturbed soils. It is thought that this is one way that the plant can maximize its uptake of phosphorus under the harshest growing conditions. 

Flowering in this species is not a showy event. C. peregrina can be monoecious or dioecious, producing male and female catkins towards the ends of its shoots. After fertilization, seeds develop inside bristly fruits. Seed banking appears to be an important reproductive strategy for this species. One study found that germinated seeds had lain dormant in the soil for over 70 years until disturbance opened up the canopy above. It is expected that seeds of this species could exhibit dormancy periods of a century or more. 

In total, this is one spectacular species. Not only does it have a unique appearance, it is also extremely hardy and an excellent species to plant in drought-prone soils wherever it is native. I do see it in landscaping from time to time. If you encounter this species in the wild, take the time to observe it in detail. You will be happy you did!

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

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

Delayed Greening

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It goes without saying that leaves are vital to the existence of any photosynthetic plant. They are, after all, the food making organs. This is why plants go to great lengths to protect them. Losing leaves can be extremely costly. One of the most intriguing methods of anti-herbivory in plants is known as delayed greening. Flushes of new growth bathed in reds, whites, and light greens can color forests from top to bottom. 

Delayed greening is a matter of resource conservation and herbivore protection. The cellular machinery that makes photosynthesis possible is costly to produce. It requires large amounts of nutrients, such as nitrogen and phosphorus, that are often in short supply. If a plant can help it, its best to avoid losing a leaf chock full of these precious materials. Delayed greening does just that. 

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Essentially, the process proceeds exactly as it sounds. Young shoots and leaves gradually expand over time, becoming more green as they grow tougher and better defended. When a plant packs its leaves full of photosynthetic machinery right out of the gates, when leaves are small and tender, it runs the risk of loosing all of its investment to a hungry herbivore. In contrast, non-photosynthetic leaves are thought to be less palatable to herbivores because they simply do not have the nutritional content of photosynthetic leaves.

By delaying the development of chlorophyll until the leaf is fully expanded and a bit tougher, some plants are maximizing the chances of successfully increasing their photosynthetic capacity over time. Research has shown that plants that exhibit the delayed greening strategy experience significant reductions in the amount of herbivory over time. What they lose with the lack of photosynthesis early on they make up for in the fact that such leaves last longer.  

Photo Credits: [1] [2]

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