Floral Pigments in a Changing World

Photo by moggafogga licensed under CC BY-NC-ND 2.0

Flowers paint the world in a dazzling array of colors. Some of these we can see and others we cannot. Many plants paint their blooms in special pigments that absorb ultraviolet light, revealing intriguing patterns to pollinators like bees and even some birds that can see well into the UV part of the electromagnetic spectrum. UV absorbing pigments do more than attract pollinators. They can also protect sensitive reproductive organs from UV radiation. By studying these pigments, scientists are finding that many different plants are changing their floral displays in response to changes in their environment.

Growing up I heard a lot about the hole in the ozone layer. Prior to the 1980’s humans were pumping massive quantities of ozone-depleting chemicals such as halocarbon refrigerants, solvents, and chlorofluorocarbons (CFCs) into the atmosphere, creating a massive hole in the ozone layer. Though ozone depletion has improved markedly thanks to regulations placed on these chemicals, it doesn’t mean that life has not had to adapt. As you may remember from your grade school science class, Earth’s ozone layer helps protect life from the damaging effects of ultraviolet radiation. UV radiation damages sensitive biological molecules like DNA so it is in any organisms best interest to minimize its impacts.

UV absorbing pigments in floral tissues can do just that. In addition to attracting pollinators, these pigments act as a sort of sun screen, reducing the likelihood of damaging mutations. By studying 1,238 herbarium specimens collected between 1941 and 2017 representing 42 different species, scientists discovered a startling change in the amount of UV pigments produced in their flowers.

Exemplary images for a species with anthers exposed to ambient conditions, Potentilla crantzii (A–C) and a species with anthers protected by floral tissue Mimulus guttatus (D–F). Darker petal areas possess UV-absorbing compounds whereas lighter areas are UV reflective and lack UV-absorbing compounds. (B) and (E) display a reduced area of UV-absorbing pigmentation on petals compared to (C) and (F). Arrows in (E) and (F) highlight differences in pigment distribution on the lower petal lobe of M. guttatus. [SOURCE]

Across North America, Europe, and Australia, the amount of UV pigments produced in the flowers tended to increase by an average of 2% per year from 1941 to 2017. These increases in UV pigments occurred in tandem with decreases in the ozone layer. It would appear that, to protect their reproductive organs from harmful UV rays, many plants were increasing these protective pigments.

However, changes in UV pigments were not uniform across all the species they examined. Plants that produce saucer or cup-shaped flowers experienced the greatest increases in UV pigments. This makes complete sense as this sort of floral morphology exposes the reproductive organs directly to the sun’s rays. The pattern reversed when scientists examined flowers whose petals enclose the reproductive organs such as those seen in bladderworts (Utricularia spp.). UV pigments in flowers that conceal their reproductive organs actually decreased over this time period.

The reason for this comes down to a trade off inherent in UV pigments. Absorbing UV radiation is a great way to reduce its impact on sensitive tissues but it also leads to increased temperatures. For plants that enclose their reproductive organs within their petals, this can lead to overheating. Heat can also be very damaging to floral structures so it makes complete sense that species with this type of floral morphology would demonstrate the opposite pattern. By reducing the amount of UV absorbing pigments in their flowers, plants like bladderworts are able to minimize the effect of increased radiation and temperatures that occurred over this time period.

How changes in floral pigments are affecting pollination rates for these plants is another story entirely. Because UV pigments also help attract certain pollinators, there is always a chance that the appearance of some of these flowers may also be changing over time. Now that we know this is occurring across a wide range of unrelated plants, research can now be aimed at tackling questions like this.

Photo Credits: [1] [2]

Further Reading: [1]

Trees In Spring

Spring is a wonderful time to observe trees. After a long, dreary winter they burst into action. For many species, spring is the time for reproduction.

Species in this episode:

-Serviceberry (Amelanchier sp.)

-Norway maple (Acer platanoides)

-Eastern redcedar (Juniperus virginiana)

-Sugar maple (Acer saccharum)

-Saucer magnolia (Magnolia x soulangeana)

Producer, Writer, Creator, Host: Matt Candeias (http://www.indefenseofplants.com)

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

Floral Mucilage

Photo taken in Monteverde, Costa Rica. Author: Cody Hinchliff, 2004. Licensed under CC BY-SA 3.0

Spend enough time around various Bromeliads and you will undoubtedly notice that some species have a rather gooey inflorescence. Indeed, floral mucilage is a well documented phenomenon within this family, with something like 30 species known to exhibit this trait. It is an odd thing to experience to say the least.

The goo takes on an interesting consistency. It reminds me a bit of finding frog spawn as a kid. Their brightly colored flowers erupt from this gooey coating upon maturity and the seeds of some species actually develop within the slimy coating. Needless to say, the presence of mucilage in these genera has generated some attention. Why do these plants do this?

Some have suggested that it is a type of reward for visiting pollinators. Analysis of the goo revealed that it is 99% water and 1% carbohydrate matrix with no detectable sugars or any other biologically useful compounds. As such, it probably doesn't do much in the way of attracting or rewarding flower visitors. Another hypothesis is that it could offer antimicrobial properties. Bromeliads are most often found in warm, humid climates where fungi and bacteria can really do a number. Again, no antimicrobial compounds were discovered nor did the mucilage show any sort of growth inhibition when placed in bacterial cultures.

It is far more likely that the mucilage offers protection from hungry herbivores. Flowers are everything to a flowering plant. They are, after all, the sexual organs. They take a lot of energy to produce and are often brightly colored, making them prime targets for a meal. Anything that protects the flowers during development would be a boon for any species. Indeed, it appears that the mucilage acts as a physical barrier, protecting the developing flowers and seeds. One study found that flowers protected by mucilage received significantly less damage from weevils than those without mucilage.

The mucilage could also provide another benefit to Bromeliads. Because these plants rely on water stored in the middle of their rosette (the tank, as it is sometimes called), some species may also gain a nutritional benefit as well. Bromeliad flowers emerge from this central tank so anything that gets stuck in the mucilage may eventually end up decomposing in the water. Since nutrients are absorbed along with the water, this could be an added meal for the plant. To date, this has not been confirmed. More work is needed before we can say for sure.

Photo Credit: [1]

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

Closed on Account of Weather

Photo by Alpsdake licensed under CC BY-SA 3.0

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]

Mighty Magnolias

Magnolias are one of those trees that even the non-botanically minded among us will easily recognize. They are one of the more popular plant groups grown as ornamentals and their symbolism throughout human history is quite interesting. But, for all this attention, few may realize how special magnolias really are. Did you know they they are one of the most ancient flowering plant lineages in existence?

Magnolias first came on to the scene somewhere around 95 million years ago. Although they are not representative of what the earliest flowering plants may have looked like, they do offer us some interesting insights into the evolution of flowers. To start with, the flower bud is enclosed in bracts (modified leaves) instead of more differentiated sepals. The "petals" themselves are not actually petals but tepals, which are also undifferentiated. The most striking aspect of magnolia flower morphology is in the actual reproductive structures themselves.

Magnolias evolved before there were bees. Because of this, the basic structure that makes them unique was in place long before bees could work as a selective pressure in pollination. Beetles are the real pollinators of magnolia flowers. The flowers have a hardened carpel to avoid damage by their gnawing mandibles as the feed. The beetles are after the protein-rich pollen. Because the beetles are interesting in pollen and pollen alone, the flowers mature in a way that ensures cross pollination. The male parts mature first and offer said pollen. The female parts of the flower are second to mature. They produce no reward for the beetles but are instead believed to mimic the male parts, ensuring that the beetles will spend some time exploring and thus effectively pollinating the flowers.

It is pretty neat to think that you don't necessarily have to track down a dawn redwood or a gingko to see a plant that has survived major extinction events. You can find magnolias very close to home with a keen eye. Looking at one, knowing that this is a piece of biology that has worked for millennia, is quite astounding in my opinion.

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

Staying Warm: An Alpine Plant Approach to Reproduction

Photo by Richard Jones licensed under CC BY-NC-ND 2.0

Things are beginning to cool down throughout the northern hemisphere. As winter approaches, most plant species begin to enter their dormancy period. Very few plants risk wasting their reproductive efforts in the chill of late fall, having gotten most of it out of the way during the warm summer months. This is easy enough for low elevation (and low latitude) plants but what about species living in the high arctic or alpine habitats. Such habitats are faced with cold, harsh conditions year round. How do plants living in these zones deal with reproduction?

These limitations are overcome via physiology. For starters, plants living in such extreme habitats often self pollinate. Insects and other pollinators are too few and far between to rely solely upon them as a means of reproduction. Also, the flowers of most cold weather plants are heliocentric. This means that, as the sun moves across the sky, the flowers track its path so that they are constantly perpendicular to its rays. This maintains maximum exposure to this precious heat source. 

Additionally, many arctic and alpine plants have parabolically shaped flowers. This amplifies the incoming radiation being absorbed by the flower. Experiments have shown that flowers that have been shaded from the heat of the sun had a dismal seed set of only 8% whereas plants exposed to the sun had an elevated seed set of 60%. 

For plants in these habitats, its all about persistence. Low reproductive rates are often offset by extremes in longevity. This is one of the many reasons why hikers must remember to tread lightly in these habitats. Damages incurred by even a single careless hiker can take decades, if not centuries, to recover. 

Photo Credit: [1]

Further Reading: [1]

Color Changing Asters

Fall is here and the asters are out in force. Their floral displays are some of the last we will see before the first fall frost takes its toll. Their beauty is something of legend and I could sit in a field and stare at them for hours. In doing so, an interesting pattern becomes apparent. Have you ever noticed that the disc flowers of the many aster species gradually turn from yellow to red? Whereas this certainly correlates with age, there must be some sort of evolutionary reason for this.

Indeed, there is. If you sat and watched as bees hurriedly dashed from plant to plant, you may notice that they seem to prefer flowers with yellow discs over those with red. The plot thickens. What about these different colored discs makes them more or less appealing to bees desperately in need of fuel? The answer is pollen.

A closer observation would reveal that yellow disks contain more pollen than those with red discs. Of course, this does relate to age. Flowers with red discs are older and have already had most of their pollen removed. In this way, the color change seems to be signaling that the older flowers are not worth visiting. Certainly the bees notice this. But why go through the trouble of keeping spent flowers? Why not speed up senescence and pour that extra energy into seed production?

Well, its all about cues. Bees being the epitome of search image foragers are more likely to visit plants with larger floral displays. By retaining these old, spent flowers, the asters are maintaining a larger sign post that ensures continued pollinator visitation and thus increases their chances of cross pollination. The bees simply learn over time to ignore the red disc flowers once they have landed. In this way, they maximize their benefit as well.

Further Reading: [1]

What is the Most Common Flower Color?

Photo by Mor licensed under CC BY-NC 2.0

Have you ever wondered what the most common flower color is? If one were to tally up all the known flowering plants, what color or colors would come out on top? I have pondered this time and again and I for some reason have a bias towards yellow. I think it is a symptom of where I live. In fact, I think flower color in general can, in part, be considered a function of geographic location. Each region of the world has its own specific pollinators driving selection for flower color. I decided to finally try and track down an answer to this question. 

The truth of the matter is, no one really knows. There is simply no database out there that fully characterizes all the colors flowers can be, let alone rank them by abundance. When you really think about it in the context of real world examples, it makes sense that this would be a daunting task. The first question becomes "how do we define the color of a flower?" This may seem silly but think about it. How many times has a field guide said one thing and reality says another? This is the main reason I don't use Peterson's Field Guide to Wildflowers. Colors vary from genus to genus and heck, they even vary within a species. A plant growing in one area may look one way while the same species growing in another area can look totally different. Far from being simply a function of genes, flower color can be just as dependent on growing conditions. 

Also, what one botanist calls red may not be what everyone else calls red. Barring a persons ability to see all of the visible light spectrum, there is no set standard, for flowers at least, as to where we draw the lines between colors. What we end up with at the end of the day are lumped packages of color pertaining to a chunk of the spectrum visible to us. It is actually an easier question to ask "what is the rarest flower color?" To that, most botanists will probably say black. To the best of my knowledge, there is only one species of plant in the world with truly black flowers. The rest are more accurately deep shades of red or purple. True blue is another rare color among flowers for the same reason. 

After a few hours (more than I should have dedicated to the cause) I came up with one satisfying answer and to sum it all up, I will put it this way: We simply have no idea what the most common flower color is in the world but it's probably green. We tend to only pay attention to the showiest flowers. Big or small, we like bright colors and we like weird colors. All the rest just get glazed over. In reality, many plant species, especially trees, produce small, non-descript green flowers. For this reason I would say that green is a safe default until someone or a group of someones puts in the time that would be needed to put any meaningful numbers to this inquiry.

Photo Credit: Mor (http://bit.ly/1y0WnJd)

American Witch Hazel

With October nearly over, temperatures are starting to dip. The asters and goldenrods have traded their floral displays for their wind-dispersed seeds that take advantage of the fall breeze. Alas, floral displays in the northern hemisphere are nearly over. There is one major show left for those living in eastern North America. From October through November (and even into December in some regions) one species of understory shrub puts forth a display reminiscent of a firework extravaganza if the fireworks only came in yellow.

I am, of course, talking about American witch hazel (Hamamelis virginiana). This wonderful shade-loving shrub goes largely unnoticed throughout the summer. Come fall, however, it makes up for its subtle appearance by offering up some of the last flowers of the season. Seemingly overnight their branches become adorned with unique little flowers whose petals shoot out like four little party streamers. They somehow manage to look both modest and showy all at once.

It may seem strange for any plant to be flowering so late. What possible advantage could this entail? Some experts believe that late flowering evolved as a way for American witch hazel to avoid competition with other flowering plants. Indeed, it certainly attracts its fair share of pollinators in desperate search of a late season meal. Flies and bees make up a majority of pollinator visits. It could also be possible that American witch hazel flowers so late to avoid hybridizing with its spring-flowering cousin, the Ozark witch hazel (Hamamelis vernalis). Regardless of its "intentions," this fall flowering strategy comes at a cost.

Despite garnishing a fair amount of pollinator attention, American witch hazel doesn't have enough time following pollination to produce fruit before winter hits. As such, fertilization of the ovaries is delayed until May the following year. The fruits, which are contained in woody capsules, spend the entire growing season maturing into viable propagules. Once mature, the seed capsules begin to dry until they become so taught that the capsule bursts. If you are lucky and attentive enough, you may be able to hear a small snap as the seeds are forcibly ejected from the capsule.

What's more, fruit set in this species is rather low. Analyses of over 40,000 witch hazel flowers showed that less than 1% produced viable seeds. Despite all of this, American witch hazel is nonetheless a successful species in eastern North American forests. It is proof that evolution need not be all or nothing. Any slight advantage is still an advantage. This hardy shrub is, at the end of the day, a survivor.

Further Reading:
http://www.amjbot.org/content/89/1/67.abstract

Colorful Claytonia

If you live where spring beauty, specifically Claytonia virginica, is native, then you may have noticed great variations in flower color. We all know the influence pollinators can have on flower shape and color but how do we explain populations with such a spectrum?

Like me you might be thinking that it is related to its growing conditions. Well, researched based out of Indiana University would suggest otherwise. It turns out, the variety of flower color in Claytonia has to do with opposing natural selection from herbivores and pathogens.

In a 2 year study, researchers made some amazing discoveries about how herbivores, pollinators, and pathogens can interact to produce the variety of flower colors one can find in any given Claytonia population. First, they made sure that Claytonia flower color is not a result of soil pH or anything like that by growing a ton of them in different conditions. They were able to demonstrate that flower color is indeed genetic and is controlled by a couple different compounds. Crimson coloring comes from a compound called "cyanidin" and white colors comes from two flavonols, "guercetin" and "kaempferol". Researchers then used spectrometry to analyze flower colors throughout the population and found 4 distinct color morphs ranging from all white to mostly crimson.

As it turns out, the flavonol compounds have pleiotropic effects in Claytonia. While they do produce white pigments, they also help defend the plants against herbivory and pathogens. Researchers then used a multitude of different analytical methods to assess overall fitness of each color morph and the results are jaw-droppingly cool to say the least.

Fitness of Claytonia was measured as total fruit production and total seed set. Because Claytonia needs a pollinator to visit the plant in order to produce fruit and set seed, reproduction is directly linked to pollinator preference. This research showed that pollinators, which for Claytonia are solitary bees, do, in fact, prefer crimson color morphs. This helps to explain the greater number of crimson colored flowers in in many populations because the more pollinators that visit a flower, the higher overall fitness for that plant. What it does not explain though, is why white morphs exist in the population at all.

As stated above, the flavonols that produce white pigmentation also beef up the plants defenses. It was found that white colored flowers experienced significantly less predation than crimson flowers. This is big news because herbivory has serious consequences for Claytonia. Plants that receive high levels of herbivore damage are far more likely to die. Because of this, white morphs, even with significantly less reproductive fitness, are able to maintain themselves in any given population.

If you're at all like me then you may need to pick you jaw up off the ground at this point. But wait! It gets cooler.... In areas where other white flowering plants like Stellaria pubera abound, white Claytonia morphs are even more rare. Why is this exactly? Well, this is due to a push towards a more pollinator-mediated selective pressure. In areas where many plants share the same flower color, it pays to be different. This causes a selective pressure in these Claytonia populations to favor even more crimson color morphs.

Isn't evolution amazing?

Further Reading:

http://bit.ly/1QxVy5Q

http://plants.usda.gov/java/profile?symbol=clvi3

Sweet Nectar

Plants produce some serious chemical cocktails. Any compound that a plant produces that isn't involved in growth or reproduction is coined a secondary metabolite. These compounds often function as herbivore deterrents. We humans are well aware of this fact and have been utilizing plants as medicine for millennia. Though the human animal may appear unique in this aspect, self-medicating has nonetheless been discovered in many other animals. Everything from monkeys to birds and even elephants seek out specific plants for things like parasite control and birthing. A study published in 2015 suggests that using plants as medication may even extend to insects. 

It has been documented that for a multitude of plant lineages, secondary metabolites are not restricted to vegetative structures. Many species produce secondary metabolites in their nectar. One interesting example of this can be found in coffee trees (Coffea sp.). These plants produce caffeinated nectar that has shown to keep bees coming back for more, not unlike we humans frequent our coffee pots. Plenty of other plants are doing this as well. Everything from amino acids, alkaloids, phenolics, glycosides, terpenoids, and even microRNA have turned up in the nectar of different plant species.

Researchers wanted to know if these chemicals may be benefiting pollinators. By isolating the different compounds, researchers found that bumblebees drinking from these flowers had drastically reduced parasite loads, specifically the gut parasite Crithidia. About half of the compounds tested were implicated in reducing parasite load but one group in particular stood out - the tobacco alkaloids. 

Alkaloids such anabasine are not limited to tobacco plants. They can be found in the nectar of trees like the basswoods (Tilia sp.) and forbs like the turtle heads (Chelone sp.). Bees that drank nectar containing these alkaloids saw parasite reductions of upwards of 80%. However, like any viable medicine, there were side effects. The eggs of bees that drank these compounds took considerably longer to develop and hatch. This cost may be well worth the lower parasite transmission rates and likely do not pose considerable selective pressures.

Whether or not bees are specifically targeting these plants for their anti-parasite properties remains to be seen. More recent work has found that we must be tentative in our conclusions at this point. Tests on other nectar compounds have shown no benefit to pollinators. Either way, these findings have opened up a whole new door into the interactions between plants and their pollinators. 

Further Reading: [1]  [2]

Time

There is something very special about old plants. They offer us a way of appreciating a timescale that we can never fully understand. I am especially fond of finding people who have had house plants in their family for generations. I grew up with a few that had already been around for decades before I was born. Here is a wonderful example of what I am talking about. This Acronia titan orchid has been blooming for years and has acquired a wonderful little moss patch in the crux of its leaf. Out of that moss grows a fern.

This photo comes to us courtesy of Kevin Holcomb. You can find him on instagram via @orchid_beard

Amber Fossils of Grain

In what may be one of the most interesting fossil discoveries in recent years, scientists from Oregon State University have described the earliest fossil evidence of grasses. Encased in 100 million year old amber this ancient grass spikelet suggests grasses were already around in the early to mid Cretaceous period. This is some 20 to 30 million years earlier than previous estimates for grass evolution. If that isn't cool enough, the grass appears to have been infected by a fungus related to ergot (the darker portion at the top), showing that this parasitism may be as old as grasses themselves. 

We humans have a long history with ergot's fondness for grasses. It is best known for producing the chemical precursors of LSD (as well as many other useful drugs) and has been implicated in some major historical events throughout our short time on this planet. However, suggesting that dinosaurs were getting high off the stuff is pushing it. Ergot likely evolved its chemical cocktail to deter herbivores from eating the grasses that it parasitizes. It has a bitter taste and cattle are said to avoid grasses that have been infected by it. It is quite possible that dinosaurs probably did the same thing. 

Either way, this finding represents a major milestone in the understanding of one of the most important plant families on the planet. Following the mass extinction at the end of the Cretaceous, grasses quickly rose to dominate roughly 20% of global vegetation. This little piece of amber now suggests that dinosaurs and their neighbors likely had a role in shaping this plant family. 

Photo Credit: Oregon State University

Further Reading: [1]

Plant Bits

Begonia cultivar

Epidendrum denticulatum 

Unknown fern

Euphorbia sp. 

Crassula sp.  

Oncidium sp.  

An Abominable Mystery

Photo by Shizhao licensed under CC BY-SA 2.5

We all love flowers but for all the attention we pay them, their origin remains elusive. Darwin called their sudden appearance in the fossil record an “abominable mystery.” Since Darwin's time, we have been able to clarify that picture a little bit. Even so, our understanding of the origin of the angiosperm lineage is dubious at best. When and why did flowers evolve?

For millions of years the land was dominated first by ferns and their allies and then by gymnosperms like cycads and gingkos. It was not until the Cretaceous that angiosperms began to rise to their current place as the dominant and most diverse group of plants. Their sudden appearance on the scene has been largely shrouded in mystery. There is scant fossil evidence to illustrate the early evolutionary steps in this development of flowers. Many paleobotanists believed that flowers had their origin in shrub-like ancestors of gymnosperms. Others felt that the origin of flowers belonged with the seed ferns (http://bit.ly/1zKfriM).

Around 2001 a fossil discovery from Yixian Formation, Liaoning, China was believed to have changed all of that. A researcher by the name of Ge Sun had stumbled upon a very primitive looking fossil plant. To his surprise, the reproductive structures seemed to show stamens in pairs below carpels and a lack of petals and sepals. The formation in which the fossil was found dated back to the Jurassic period. Could this represent the remains of the earliest flowers?

The fossil has been coined Archaefructus and since its discovery at least two species have been identified. Archaefructus was an aquatic plant, likely living on the edge of freshwater lakes. These fossils (as one would expect) are quite contentious. Some argue that it is more derived than would be expected from the first flower. Recently it has been suggested that Archaefructus is a sister lineage to early flowering plants, not unlike Nymphaeales or Amborella living today. 

What Archaefructus does suggest is that flowers had their origin much earlier than the Cretaceous. Other discoveries from the same formation (ie. Archaeamphora longicervia) suggest that flowering plants were already diversifying at this time. So, if this is the case, when did flowers appear on the scene? Far from the smoking gun that a fossilized flower would represent, researchers are nonetheless finding tantalizing fossil evidence that places the origin of flowering plants all the way back to the Triassic. 

By examining Triassic microfossils, some researchers believe they have found fossilized pollen grains that are distinctly angiosperm in origin. I won't go into it here but extant examples show a major distinction between pollen from gymnosperms and pollen from angiosperms. If this is true, flowers may be way older than ever expected. For now, the jury is still out on this one. 

Flowers evolved for sex. We associate animals like bees, bats, and birds with flowers today but most of these lineages came much later in the game. Exactly what was around pollinating early flowers remains a bit of a mystery as well. Were the earliest flowers wind pollinated or was there some insect or even reptile that served the selection pressure necessary for their evolution? Only time and more fossil discoveries will tell. 

Photo Credit: Shizhao (Wikimedia Commons)

Further Reading:

http://www.sciencemag.org/content/296/5569/899.abstract?ck=nck&siteid=sci&ijkey=8dZ6zTqF606ps&keytype=ref

http://faculty.frostburg.edu/biol/hli/research/Eoflora.pdf

http://www.ohio.edu/people/braselto/readings/angiosperms.html

http://journal.frontiersin.org/Journal/10.3389/fpls.2013.00344/full

http://www.amjbot.org/content/96/1/5.abstract

Cannonball!

Photo by Joel Abroad licensed under CC BY-NC-SA 2.0

There are some trees out there that you probably shouldn't hug. Couroupita guianensis is one such example. You certainly wouldn't want to risk standing at the base of one for any length of time. What looks like a vine covering the trunk of each tree is actually the reproductive structures of this species. Beautiful flowers give way to hefty seed pods, earning this tree its common name, the cannonball tree. 

A native to Central and South America as well as parts of the Caribbean, the distinctive flowers of this tree are born on long stalks that emerge right out of the trunk. This is known as "cauliflory." Trees like this can cause you to do a double take. Indeed, it is strange seeing flowers on a trunk instead of at the tips of branches. It is likely that this type of flowering has evolved as a form of resource partitioning. Instead of vying for pollinators or seed dispersers way up in the canopy, trees like C. guianensis may opt for them at lower levels in the forest where competition may be lower. 

In the case of C. guianensis, the main pollinators are carpenter bees. The peculiar flowers don't produce any nectar, however, they make up for this by offering copious amounts of pollen. The strangest aspect of this is that two different type of pollen are produced. Each flower has two sets of anthers, one set forms a ring around the center of the flower and the other set is located at the tip of the petal that is bent inward forming a hood. What's more, the pollen grains produced by each set differs in appearance with the ring pollen being white and smaller and the hood pollen being yellow and larger. As it turns out, the hood pollen is mostly sterile whereas the ring pollen is fertile. When a bee lands on the hood of the flower looking for pollen, it is attracted to the larger grains. As it harvests pollen from the hood its body is pushed up against the ring pollen, which is carried to the next flower, where the process is repeated and the flower fertilized.

Photo by Mauricio Mercadante licensed under CC BY-NC-SA 2.0

After fertilization, large capsules are produced that sort of resemble coconuts or canon balls. Being a member of the Brazil nut family, these capsules can measure upwards of 8 inches in diameter and are chock full of pulp and seeds. Each capsule eventually falls from the tree, cracking open as it smashes into the ground. The capsules can be so large and heavy that anyone unfortunate enough to be standing under one when it fell is likely to be killed by the impact. The pulp inside is said to smell quite awful, which is a attractive to various seed dispersers around the forest.  Peccaries as well as large rodents like the paca eat the seeds, which germinate quite well after passing through their gut. 

Couroupita guianensis has been planted far outside of its natural range for a variety of reasons. It is likely that anyone visiting a botanical garden in the tropics will come across one of these odd trees. Any gardener worth their weight would do well to keep this tree away from footpaths. This is a species best admired from a distance. Aside from avoiding a head crushing blow from one of those seed capsules, this is a tree that must be seen in its entirety to truly appreciate. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

Cast In Iron

Photo by Phillip Merritt licensed under CC BY-NC-SA 2.0

When it comes to hardy houseplants, few species can hold a candle to the Aspidistra. With their ability to tolerate dismal lighting conditions and less than stellar air quality, it is no wonder the this genus was a favorite among the middle class during the Victorian era. They were so common during that time period that George Orwell himself used them as a metaphor in his 1936 novel "Keep the Aspidistra Flying." Today they are nothing more than space fillers. Commonly known as "cast iron plants," they are a natural step up from silken foliage in waiting rooms and cubicles. They can virtually be ignored and still maintain their composure. For a houseplant, this is pretty incredible. However, this genus did not originate in the home. It is just as wild as any other plant out there. What are the Aspidistra and where do they come from?

Photo by justinleif licensed under CC BY-NC-SA 2.0

With their long, strap-like leaves that seem to pop out of the dirt at random, it is not readily apparent that these plants belong to the same family as asparagus - Asparagaceae. Since the 1980's, botanists have described upwards of 93 different species within the genus. They are native to eastern Asia and hit their peak diversity in China and Vietnam. Many species within this genus are endemic to these areas. 

Photo by Scott Zona licensed under CC BY-NC 2.0

Aspidistra as a whole are understory species, growing on the ground underneath dense canopies of trees and shrubs. This is why they can adapt so well to the low light conditions of homes and offices. Though they are mostly tropical in nature, Aspidistra have been known to cope with temperatures as low as −5 °C (23 °F). Despite their leafy appearance, Aspidistra have surprisingly beautiful flowers. You just have to know where to look. 

Flowers are produced at the base of the plant. They are often covered by litter and soil. Despite their cryptic nature, they are nonetheless incredibly beautiful and complex. The flowers are spider-like with a large flattened stigma. They are also the key to identifying different species. Their pollinators are thought to consist mostly of flies, beetles, and the occasional fungus gnat. There is some evidence that some species of Aspidistra are even pollinated by amphipods in the soil. If this is true, it is surely one of the most unique pollinator syndromes ever discovered. 

So, there you have it. One of the most commonly kept and ignored houseplants just happens to be quite interesting. Every plant has an evolutionary and ecological history that has shaped its kind over millennia. It just goes to show you that even the most common houseplants have a story to tell. Think about that next time you come across these growing in a stuffy waiting room. 

Photo Credit: justinleif (http://bit.ly/1srlbwk), scott.zona (http://bit.ly/1wQMdcZ), Phillip Merritt (http://bit.ly/14Rcbph)

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