Blue

Blue is a strange color. This may seem like an odd statement yet, when you think about it, so few things in nature are truly blue. It is estimated that, of all the colors plants utilize to attract pollinators, blue only occurs in less than 10% of species. This isn't a pattern restricted to plants either. Blue is an infrequent occurrence throughout the biological world.

When it does appear, the color blue is usually the result of structure rather than pigment. The feathers of a bluejay, the wings of a morpho butterfly, and the sheen of a beetle's elytra - these blues owe their vibrancy to refracted light, not pigment. Without light, the crystalline cells responsible for the blue hue would appear dull brown. As light enters their structure, it is bent in a way that gives off blue wavelengths.

Plants have adopted this strategy as well. The berries of Pollia condensata use a similar crystalline structure that results in blue. However, there are true blue flowers out there. How have species with blue flowers managed to overcome the rarity of blue pigments?

The simple answer is that they haven't. There are no blue pigments in the floral world. Instead, plants utilize what can only be described as an evolutionary hack. Blue flowers obtain their color by doing something we all did in art class, blending pigments (similar to the one true black flower http://bit.ly/1FDmU8l). By producing varying amounts of anthocyanins (the pigments responsible for reds) floral cells are able to make blue flowers.

The anthocyanins can also be tweaked to appear blue. One way of doing this is through changes in pH. Blue petunias, for example, have a defect in the proton pumps found inside their flower cells. This causes the cells to become more basic than acidic, which manifests in blue, rather than purple, flowers.

Despite the lack of blue in the floral world, it nonetheless seems to work well when it comes to pollinators. I watched multiple different species of bee visit the flowers of this downy gentian (Gentiana puberulenta). Hummingbirds often visit the amazing floral display produced by the great blue lobelias (Lobelia siphilitica) in my garden. Anyone that has looked over a patch of blue lupine or delphiniums can attest to the success of this color.

Further Reading:
http://www.sciencedirect.com/…/article/pii/S2211124713007547

True Black

Black seems to go with everything. It is a sleek and powerful color. This is a fact not lost on many plant breeders. Much work has been done to produce flower varieties that exhibit pure black coloration. This is not an easy task as true black is not a pigment that plants have readily available to utilize. By breeding plants with increased amounts of anthocyanin pigments in their petals, breeders have been able to produce some varieties that are either so red or so violet that, to us, they appear jet black. It was long thought that all black flowers simply did not exist in the wild but a gentian from Central America blows that assumption out of the water.

Meet Lisianthius nigrescens. Often referred to as the “Flor de Muerto,” this striking gentian produces the most extraordinarily jet black flowers known in the plant kingdom. Indeed, researchers have looked at the pigments responsible for the black coloration and found that they do in fact absorb all wavelengths in the visible spectrum of light. Thus these flowers are truly black.

It was suspected that, with their long, tubular shape, they must attract animals like hummingbirds for pollination and therefore must emit light high in UV wavelengths. Nope. Other pigments in the flowers also absorb all UV light. These flowers are about as black as it gets! Field observations actually found that bees are the primary pollinators of this species. Whats more, the flowers are virtually scentless. How exactly this plant attracts pollinators remains a mystery, a fact I much enjoy about the natural world.

Photo Credit: Lauren Zarate and the Biodiversity Heritage Library http://www.projectnoah.org/spottings/37532042

Further Reading: http://www.znaturforsch.com/ac/v59c/s59c0625.pdf

 

Better if Browsed?

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Behold the glory and splendor of scarlet gilia (Ipomopsis aggregata)! This gorgeous species is native to much of western North America from British Columbia south to Texas. Far from being just a beautiful red wildflower, scarlet gilia has some life history traits that are quite fascinating. Did you know that there is some evidence to suggest that this species actually benefits from natural levels of herbivory?

We are all too familiar with herbivore damage. Countless times I have been awaiting a bloom to burst only to have the buds nipped off the night before they opened. While this can be devastating to most plant life (not to mention my sanity), for scarlet gilia, an encounter with a hungry deer may actually increase its reproductive fitness! Scarlet gilia is most often a biennial. It spends its first year photosynthesizing as a rosette, saving up energy for next year's reproductive effort. Starting in July of its second year, most scarlet gilia will throw up a single flower stalk. In at least one study, 77% of flowering plants were dined upon. Whereas this would spell disaster for most other flowering plants, the removal of the single flower stalk stimulates the production of, on average, 5 new flowering stalks.

Each new flowering stalk sees no decrease in fitness either. This means that each plant that gets browsed subsequently benefits from a five fold increase in reproductive ability. Interestingly enough, plants that have already been browsed once don't seem to be browsed again. It is believed that the initial browsing signals the plant to begin producing secondary compounds that render its tissues either distasteful or even toxic. Some authors suggest that this increase in fitness due to herbivory is site specific and only will occur at highly productive areas. More work needs to be done to shed light on this matter.

Just when you thought scarlet gilia couldn't get any cooler, now we will consider pollinators. A cursory glance will suggest that the long, red, tubular flowers are pollinated by hummingbirds. This is true, at least for part of the year. Scarlet gilia blooms from July through September but its hummingbird pollinators are gone by the end of August. Why would the plant continue to flower after its pollinators have left? If you were to watch a patch of scarlet gilia from July until September, you would notice that, on average, flowers produced from July to August are deeper red than those produced after August, which are much paler with white spots. 

What is happening is the plant is switching its cues. Whereas hummingbirds are attracted to red, moths on the other hand are attracted to flowers towards the white end of the spectrum. After the hummingbirds migrate south, scarlet gilia produce lighter colored flowers to take advantage of white-lined sphinx moths, which are available for pollination well into September. WOW!

Further Reading:

http://www.life.illinois.edu/paige/overcomp.html

http://www.uvm.edu/~biology/Classes/269/juengerberg97.pdf

http://eco.cellsignal.com/04/scarlet.html

http://plants.usda.gov/core/profile?symbol=ipag

http://raveneditions.com/columbia-gorge-flowers/skyrocket/

A Case of Sexual Fluidity in the Plant World

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In humans, sex is determined at fertilization. The embryo receives either an X or a Y chromosome. Many other organisms have their sex determined in a manner similar to this as well. The case with plants is not so rigid. Many plants produce both male and female parts on the same flower, others have flowers that are either male or female, while some can change their sex throughout their lifetime. The latter is quite interesting and offers an insight into the differences in maleness and femaleness. 

The green dragon (Arisaema dracontium) is an arum related to jack-in-the-pulpit. It is wide spread throughout the east but declining in much of its northern range. This species produces a single inflorescence that can be purely male, both male and female, or, in some rare cases, entirely female. The mechanism for this has been a subject of interest for many botanists as it does not seem to be dictated solely by genetics. It has been discovered that any given plant may switch up its flowering strategy from year to year.

What researchers have found is that male flowers are most often produced in younger plants as well as plants that are stressed. In years where environmental conditions are not as conducive to survival or if the plants have not had enough time to build up energy reserves, it is not uncommon to find only male plants. This is advantageous since male flowers and pollen are a lot less costly to produce than ovaries. Also, the plant does not have to allocate resources into developing seeds. In good years and also in older, larger plants, inflorescence are produced that are both male and female. If the plants are less stressed and large enough, more energy can be allocated to seed production. In some rare cases, very large plants have been known to produce only female flowers. This seems to be a strategy that is adopted only under the best of conditions. 

It should be noted that whereas there seems to be a threshold for environmental conditions as well as plant size in determining what kinds of flowers will be produced, each green dragon population seems to vary. In essence there is some genetic determination for how the plant will respond in any given year but this is where teasing the gene environment out of the actual environment gets tricky. Studying these plants is giving us more insight into the advantages and disadvantages of each sex as well as helping to inform how sensitive species like the green dragon will respond in a changing climate. 

 

Further Reading:

http://plants.usda.gov/core/profile?symbol=ardr3

http://www.jstor.org/stable/2656980

http://www.jstor.org/stable/2445597?seq=1

Cleistogamy

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In the wild, plants are not always found growing under ideal conditions. Often, many plant species find themselves on the fringe of their habitable range. Other times, pressures like trampling or grazing cause a plant to expend a lot of energy trying to recoup for lost resources. If a plant growing under these conditions is to successfully reproduce, it has to sometimes stake its bets on self-fertilization. 

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The evolution of special flowers that never open has arisen in many different plant families. These permanently closed flowers are known as cleistogamous flowers. These are not always produced as a result of a direct environmental stress, however, and their persistence throughout so many different plant families is a bit of a puzzle to evolutionary biologists. How and why are these mixed mating systems maintained in a plant population? There must be selective advantages to both.

It has long been thought that plant populations should only stably exist as either fully opened, chasmogamous flowers, or fully closed, cleistogamous flowers. The existence of many species in which both forms exist on the same plant really threw a wrench into that hypothesis. Some examples of plants that possess such mixed mechanisms can be seen in genera such as Impatiens, Viola, and Utricularia. 

In the cases that have been studied, it was shown that cleistogamous flowers produce healthier seed with higher germination success than those of an openly pollinated chasmogamous flowers. It has also been shown that the production of cleistogamous flowers is much more economical for the plant. If flowers never open and never have to attract pollinators, then the plant doesn't need to waste energy on the production of petals, color, nectar, etc. This way, more energy can be pumped into seed production. 

The flip side to this mating system is that cleistogamy produces no genetic diversity. The plant is more or less cloning itself with every seed. This is okay if the plant is growing under challenging conditions. If the parent was able to survive long enough to reproduce then it obviously has the genetic make-up that is fit enough to survive such conditions and now, all of the cloned offspring do as well and thus all copies of its genes made it into the next generation. It is neat to think that plants kind of have this insurance policy built in to their reproductive strategy.

PHOTO NOTE: I found the picture of cleistogamous violet flowers on the following blog. It is not my picture! Please check out the blog for more!

source: http://blog.chestnutherbs.com/even-violets-need-a-plan-b

Further Reading: 

http://www.amjbot.org/content/96/11/2074.full.pdf+html?sid=41c1503d-23a8-40f8-93bf-8d849be7edec

http://www.jstor.org/discover/10.2307/1936588?uid=3739256&sid=21102186350373

http://onlinelibrary.wiley.com/doi/10.1046/j.1095-8312.2002.00039.x/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, a research paper by Frank M. Frey out of Indiana University would suggest otherwise. He chalks it all up to opposing natural selection from herbivores and pathogens.

Say what now? In a 2 year study, Frey has made some amazing discoveries. First, he 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. He found 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". Frey 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. Frey used a multitude of different analytical methods to assess overall fitness of each color morph and his 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. His research found 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 any given area because the more pollinator visits, 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. Frey found that white colored flowers experienced significantly less predation than crimson flowers. Herbivory has serious consequences for Claytonia and 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. Wow!

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, Frey explains that 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

Something Smells...

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Plant nurseries are a dangerous place for me. Well, not really me so much as my wallet. I am always on the lookout for new and interesting plant friends to bring home. I recently visited a local nursery that has 4 hoop houses worth of plants to ogle. As I was walking the crowded alleyways between row after row of botanical treasures, something tucked away in a back corner caught my eye. There was a stark juxtaposition between burgundy and deep green that I simply could not ignore. I tip toed around a variety of succulents, dracaena, and gesneriads to investigate this colorful curiosity. 

As I approached this odd little plant I realized there was a long spike jutting out of the top. Ah, so this was some sort of peperomia. At this point I could see why it was kept among succulents. The leaves of this peperomia are quite succulent. Like fat little canoes, the leaves appeared to have green window-like surfaces that quickly gave way to a red bilge. This was truly unique. I had to have it. 

Despite the fact that it was the only one of its kind, I got it for a steal. It wasn't planted very well so I had to be quite careful getting it home. Mixing up soil can be fun, especially when you know the plant you are catering to. This was not one of those cases. Regardless, the succulent nature of the plant hinted at a need for a well drained mix. Three parts gravel to one part compost should do the trick. Despite its size, the plant had an under-developed root system. This explains why it was so floppy on the ride home. Once it was in its new pot, I had to go about picking out a perfect spot on the shelf. I knew that plants like Crassulas and aloes turn colors under high light so I figured this would be my best bet at preserving the beauty of this specimen. I watered it and sat back to enjoy its beauty among all the other plants in the collection. 

Later that day I began noticing an odd smell. It wasn't necessarily offensive yet it wasn't easily ignored either. It was also restricted to one area near the plant shelf. My nose didn't reveal the source. I put shoes outside and checked the area for anything that may be starting to rot. Nothing. After a while I must have gotten used to it and after a couple hours I forgot about it. Days went by and every once in a while the smell would creep its way into my nose. I was very confused and yet too busy to be serious about locating the source. 

I like to show off my plants so I made sure to draw attention to this new peperomia any time someone dropped by for a visit. It seemed to resonate well with friends. After a series of inquiries into this plants identity I decided to do my homework. Simply referring to it as a mystery peperomia wasn't satisfying enough. Luckily the internet exists. A quick image search for "succulent red peperomia" gave me my answer. 

My beautiful plant friend was none other than Peperomia graveolens, an endemic of mountainous forests in Ecuador. To my surprise, this is not a species that enjoys a lot of sun. The burgundy undersides are thought to assist the plant in soaking up as much sunlight as possible as it ekes out a living under the canopy. I guess I was going to have to move this plant to a lower shelf. The good news is that the soil mixture I made was going to work. There was no need to disturb the meager root system any more than I already had. 

Apparently this species is only known from two wild populations. All of the plants in cultivation are descendants of collections made in 1973 by some German botanists. This is truly a special plant! As I was reading various plant care websites, a recurring theme in the writing caught my attention. The inflorescence of this species is said to have a "mousey odor." I have seen that term before but, even after years of working in pet stores, I couldn't quite picture what a mousey odor would be like. Urine perhaps? Then I realized something. That strange odor was still present in and around the plant shelf. Could this be what I was smelling? I carefully picked up the plant and gave it a sniff. Yep! There is was. I still don't think of mice when I smell it but I can see how such descriptive terms could be applied. Regardless, my introduction to this wonderful little plant has made it all the more interesting. This is one of the main reasons I keep house plants. My collection is my own little botanical garden that I fill with species that capture my imagination. 

Further Reading:

http://www.iucnredlist.org/details/45780/0

A Tenacious Little Mustard

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If you are looking to place a bet on what the first flower sighting of early spring will be, then a safe pick would be Draba verna. Known commonly as early Whitlow grass, the small stature of this tenacious mustard is quite deceiving. It is one tough cookie, certainly one of the toughest little plants I know. Though it is originally native to parts of Eurasia, encountering this little beauty after a long winter is a welcome treat. 

If you want to find this species, you have to look where humans are. It excels in disturbance. I most often see it growing along the edges of gravel parking lots. It is quite variable in appearance but is nonetheless recognizable due to its early flowering period and bright white, four petaled flowers. It is not uncommon for there to be plenty of snow still on the ground when these little plants begin throwing up flower buds. 

Like most winter weary denizens of the northern hemisphere, the flowers of Draba verna only seem to open on during bright, sunny days. There is good reason for this too. For starters, the few pollinators active this early in the season are only really out on fair weather days. Also, since dark and cloudy spring days are often cold and full of precipitation, it isn't worth the risk of damaging sensitive flower parts from wind, rain, or frost. Plants set seed by late spring but by that time ambient temperatures are too high for successful germination. Instead, seeds require a warm summer dormancy before they will begin germinating later in the fall. Sometimes the most interesting things come in very small packages. 

Further Reading:

http://plants.usda.gov/core/profile?symbol=DRVE2

http://www.jstor.org/discover/10.2307/2483459?sid=21106125483663&uid=2&uid=4