Daffodil Insights

Photo by Amanda Slater licensed under CC BY-SA 2.0

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

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

Narcissus poeticus

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

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

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

Narcissus tazetta. Photo by Fanghong licensed under CC BY-SA 3.0

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

Narcissus cyclamineus. Photo by Francine Riez licensed under CC BY-SA 3.0

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

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

Narcissus triandrus. Photo by Dave Gough licensed under CC BY 2.0

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

Narcissus viridiflorus - a green, fall-blooming daffodil. Photo by A. Barra licensed under CC BY 3.0

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

The endangered Narcissus alcaracensis. Photo by José Luis López González licensed under CC BY-SA 4.0

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

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

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

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

Are Crickets Dispersing Seeds of Parasitic Plants?

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Parasitic plants lead unique lifestyles. 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 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 dust-like as many of their relatives. They are actually very 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 necessarily 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.

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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 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]

Caliochory - A Freshly Coined Form of Seed Dispersal

Photo by Ude licensed under CC BY-SA 3.0

A new form of seed dispersal has been described. It involves birds but not in the sense we traditionally think. Everyone understands how effectively birds disperse seeds contained in small fruits such as berries, or as barbs attached to their feathers. It took finding an out-of-place patch of Japanese stiltgrass (Microstegium vimineum) for lead author Dr. Robert Warren to start looking at bird dispersal in a different light. 

While working in his yard, he noticed a patch of Japanese stiltgrass growing out of a window planter some 6 feet off the ground. Japanese stiltgrass can be highly invasive but its seeds aren't adapted for vertical dispersal. However, it does employ a mixed mating system composed of outcrossing flowers at the tips of the spikes along with cleistogamous flowers whose seeds remain on the stem. Taking out a ladder, Warren discovered that the grass was growing out of a bird nest. It would appear that stiltgrass stems containing seeds were incorporated into the nest as building material and then germinated the following year. Thus began a deeper investigation into the realm of nest seeds.

Teaming up with researchers at Yale and the United States Forest Service, they set out to determine how often seeds are contained within bird nests. They collected nests from 23 different bird species and spread them over seed trays. After ruling out seeds from potential contamination sources (feces, wind, etc.), they irrigated the nests to see what would germinate. The results are quite remarkable to say the least.

Over 2,000 plants, hailing from 37 plant families successfully germinated. In total, 144 different plant species grew from these germination trials. The seeds appeared to be coming in from the various plant materials as well as the mud used to build these nests. What's more, nearly half of the seeds they found came from cleistogamous sources. Birds whose nests contained the highest amounts of seeds were the American robbin (Turdus migratorius) and the eastern bluebird (Sialia sialis). These results have led the authors to coin the term "caliochory," 'calio' being Greek for nest and 'chory' being Greek for spread.

It has long been assumed that cleistogamous reproduction kept seeds in the immediate area of the parent plant. This evidence suggests that it might actually be farther reaching than we presumed. What's more, these numbers certainly hint that this otherwise unreported method of seed dispersal may be far more common than we ever realized. Whether or not plants have evolved in response to such dispersal methods remains to be tested. Still, considering the diversity of birds, their nesting habits, and the availability of various plant materials, these findings are quite remarkable!

Photo Credits: [1]

Further Reading: [1]

Large Parrots And Their Influence On Amazonian Ecosystems

Photo by I, Luc Viatour licensed under CC BY 2.0

Parrots, especially the larger species, have long been thought to be a bane to plant reproduction. Anyone that has watched a parrot feed may understand why this has been the case. With their incredible beaks, parrots make short work of even the toughest seeds. However, this assumption is much too broad. In fact, recent research suggests that entire Amazonian ecosystems may have parrots to thank.

Bolivia's Amazonian savannas are remarkable and dynamic ecosystems. These seasonally flooded grasslands are dotted with forest islands dominated by the motacú palm (Attalea princeps). These forest patches are an integral part of the local ecology and have thus received a lot of attention both culturally and scientifically. The dominance of motacú palm poses an intriguing question - what maintains them on the landscape?

The fruits of this palm are quite large and fleshy. Some have hypothesized that this represents an anachronism of sorts, with the large fruit having once been dispersed by now extinct Pleistocene megafauna. Despite this assumption, these forest islands persist. What's more, motacú palms still manage to germinate. Obviously there was more to this story than meets the theoretical eye. As it turns out, macaws seem to be the missing piece of this ecological puzzle. 

Researchers found that three species of macaw (Ara ararauna, A. glaucogularis, and A. severus) comprised the main seed dispersers of this dominant palm species. What's more, they manage to do so over great distances. You see, the palms offer up vast quantities of fleshy fruits but not much in the way of a good perch on which to eat them. Parrots such as macaws cannot take an entire seed down in one gulp. They must manipulate it with their beak and feet in order to consume the flesh. To do this they need to find a perch.

Suitable perches aren't always in the immediate area so the macaws take to the wing along with their seedy meals. Researchers found that these three macaw species will fly upwards of 1,200 meters to perch and eat. Far from being the seed predators they were assumed to be, the birds are actually quite good for the seeds. The fleshy outer covering is consumed and the seed itself is discarded intact. This suggests that preferred perching trees become centers of palm propagation and they have the parrots to thank. 

Indeed, seedling motacú palms are frequently found within 1 - 5 meters of the nearest perching tree. No other seed disperser even came close to the macaws. What's more, introduced cattle (thought to mimic the seed dispersing capabilities of some extinct megafauna) had a markedly negative effect on palm seed germination thanks to issues such as soil compaction, trampling, and herbivory. Taken together, this paints a radically different picture of the forces structuring this unique Amazonian community.

Photo Credits: Wikimedia Commons

Further Reading: [1]

Thanks, Ducks!

Photo by loren chipman licensed under CC BY-NC 2.0

Recent research suggests that certain duck species are crucial for maintaining wetland plant diversity in highly fragmented landscapes. Functioning wetlands are becoming more and more isolated each year. As more land is gobbled up for farming and development, the ability for plants to get their seeds into new habitats is made even more difficult. Luckily, many plants utilize animals for this job. Seeds can become stuck in fur or feathers, and some can even pass through the gut unharmed. What's more, animals can move great distances in a short amount of time. For wetland plants, the daily movements of ducks seems to be paramount. 

By tracking the daily movements of mallards, a team of researchers from Utretch University were able to quantify how crucial these water fowl are for moving seeds around. What they found was quite remarkable. In autumn and winter, the diet of mallards switches over to seeds. Not all seeds that a mallard eats get digested. Many pass through the gut unharmed. Additionally, mallards are strong flyers. On any given day they can travel great distances in search of winter foraging grounds. In the evenings, they return to roosting sites with a high degree of fidelity. 

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The research team was able to demonstrate that their movements cover even greater distances in highly fragmented landscapes. It's these daily migrations that are playing a major role in maintaining plant diversity between distant wetlands. This is especially important for wetlands that function as roost sites. Whereas mallards distribute around 7% of the surviving seeds they eat among foraging sites, that number jumps to 34% for surviving seeds at roost sites. Given the sheer number of mallards on the landscape, these estimates can really add up. 

It is likely that without mallards, North American wetlands would be much less diverse given their increasingly isolated nature. However, not all seeds are dispersed equally. Small seeds are far more likely to pass through the gut of a duck unharmed, meaning only a portion of the plant species that grow in these habitats are getting a helping hand (wing?). Still, the importance of these birds cannot be overlooked. The next time you see a mallard, thank it for maintaining wetland plant diversity. 

Photo Credits: [1] [2]

Further Reading: [1]

American Persimmon

Photo by Doug McAbee licensed under CC BY-NC 2.0

I will never forget the time I went to the grocery store and bought what I thought were strange tomato varieties. I got home and dug into them only to discover they were not tomatoes at all. I quickly realized the error in my judgment. Instead of the unmistakable flavor of a tomato, what I experienced was something slightly sweet and kind of astringent. I had inadvertently purchased a couple persimmon fruits. I was young and naive so I will cut myself some slack, however, like any good mistake, I was rewarded by the inadvertent introduction to a fascinating fruit I had never experienced before. 

Thinking this to be some strange tropical species, I was surprised to learn that North America does indeed have its own species of persimmon. Known scientifically as Diospyros virginiana, the American persimmon is native to much of the eastern U.S. but is absent north of Pennsylvania. We are lucky, biogeographically speaking, to have this species as the family to which it belongs, Ebenaceae, is predominantly tropical. It is an early successional tree species, often growing on recently abandoned farmland. In the spring this shrubby tree produces small yet attractive white and yellow flowers. American persimmon are dioecious meaning individual trees are either male or female. Their main pollinators are bees.  

As is often seen with many fruiting tree species,  there is a lot of variety between the fruits of different persimmons. They can range in size from small crabapples to the tomato-like fruits we find in the grocery store. There are those who suspect the fruits of the American persimmon to be a throwback to a time when animals like woolly mammoths and ground sloths roamed this continent, dispersing persimmon seeds as they roamed across the terrain. Indeed, fossils of American persimmon have been found in Miocene deposits in areas of Greenland and Alaska which suggests that this species has undergone range contraction, potentially due to the loss of these large seed dispersers. However, modern day evidence would seem to suggest otherwise. Today, much smaller animals like raccoons and opossum seem to do just as good of a job as a larger animal would. It is likely that the constricted range of the American persimmon has more to do with climate than seed dispersal. 

If you have never tried a persimmon before then seek one out and give it a go. If you find them in a grocery store, there is a good chance the fruit belongs to the Asian species (Diospyros kaki). The key to enjoying an American persimmon is making sure its ripe. If you are too early you are going experience some of the worst tannin dry mouth (I honestly don't think I will ever convince my mother to eat another strange fruit again). Either way, this neat species often goes overlooked until it is in fruit. Keep your eye out for fruiting persimmon in your area and report back if you decide to sample some. 

Photo Credit: Doug McAbee (http://bit.ly/1xznvPx)

Further Reading:
http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/diospyros/virginiana.htm

Bird's Foot Violet

As a life long denizen of deciduous forests, prairies and savannas present an entirely new set of stimuli. A recent excursion into an expansive oak savanna found me overwhelmed by the beauty of such places. Being mid October, the color pallet of the landscape ranged from myriad shades of reds, browns, yellows, and oranges. I was walking through a particularly sandy patch of soil when something caught my eye. A little flash of lavender shone through the amber grasses. To my astonishment I had found a plant that has managed to elude me for many years. 

What I had found was a bird's-foot violet (Viola pedata). Its deeply divided leaves, which faintly resemble a bird's foot, are unmistakable. What was even more fantastic was that this particular plant was in full bloom. I looked around and found only a small handful of other plants. This one was the only one in bloom. Though not unheard of for this time of year, I couldn't help but revel in the serendipity of the moment. 

Like all members of the genus Viola, bird's-foot violet is a photoperiodic plant. By this I mean that all aspects of its growth are sensitive to the relative amount of sunlight in any given day. Violets are generally spring time plants, however, the shortening days and cooler temperatures of fall aren't that different from spring. As such, this lovely little plant was perhaps a bit confused by the cool October weather. I didn't see any pollinators out and about but that doesn't mean that a hardy bumblebee wouldn't be lucky to stumble into its blooms. 

Back in my home state of New York, this particular species of violet is truly a rare find. The kind of habitats which it frequents have been largely destroyed. It is a xeric species that doesn't appreciate water hanging around for very long. Finding it growing in mostly sand was not surprising to say the least. Like most other violets, its seeds come complete with their own fleshy protuberance called an elaiosome. The purpose of these fatty attachments are to attract foraging ants in the genus Aphenogaster. The ants find the elaiosomes to their liking and take them back to their nest. Once the elaiosome is eaten, the seed is discarded into a refuse chamber inside the nest. There it finds a favorable microsite for germination full of nutrient-rich ant compost.

Further Reading:
http://www.jstor.org/stable/3668940?seq=1#page_scan_tab_contents

http://www.illinoiswildflowers.info/prairie/plantx/bird_violet.htm

Osage Orange

As a kid I used to get a kick out of a couple trees without ever giving any thought towards what it was. My friend's neighbor had a some Osage orange trees (Maclura pomifera) growing at the end of his driveway. Their houses were situated atop a large hill and the road was pretty much a straight drop down into a small river valley. After school on fall afternoons, we would hang out in my friends front yard and watch as the large "hedge apples" would fall from the tree, bounce off the hood of his neighbor's car (why he insisted on parking there is beyond me) and go rolling down the hill. I never would have guessed that almost two decades later the Osage orange would bring intrigue into my life yet again. This time, however, it would be because of the evolutionary conundrum it presents to those interested in a paleontological mystery...

The fruit of this tree are strange. They are about the size of a softball, they are green and wrinkly, and their insides are filled with small seeds encased in a rather fibrous pulp that oozes with slightly toxic white sap. No wild animal alive today regularly nibbles on these fruits besides the occasional squirrel and certainly none can swallow one whole. Why then would the tree go through so much energy to produce them when all they do anymore is fall off and rot on the ground? The answer lies in the recently extinct Pleistocene megafauna. 

The tree is named after the Osage tribe who used to travel great distances to the only known natural range of this tree in order to gather wood from it for making arrows. It only grew in a small range within the Red River region of Texas. When settlers made it to this continent, they too utilized this tree for things like hedgerows and natural fences. 

What is even stranger is that recent fossil evidence shows that Maclura once had a much greater distribution. Fossils have been found all the way up into Ontario, Canada. In fact, it is believed that there were once 7 different species of Maclura. It was quickly realized that this tree did quite well far outside of its current natural range. Why then was it so limited in distribution? Without the Pleistocene megafauna to distribute seeds, the tree had to rely on flood events to carry the large fruit any great distance. With a little luck, a few seeds would be able to germinate out of the rotting pulp. Botanists agree that the Red River region was a the last stronghold for this once wide ranging species until modern man came on the scene. 

Another clue comes from the toxicity of the fruits. Small animals cannot eat much of it without being poisoned. This makes sense if you are a Maclura relying on large animals as dispersers. You would want to arm your fruit just enough to discourage little, inefficient fruit thieves from making a wasteful meal out of your reproductive effort. However, by limiting the amount of toxins produced in the fruit, Maclura was still able to rely on large bodied animals that can eat a lot more fruit without getting poisoned. Today, with the introduction of domesticated megafauna such as horses and cows, we can once again observe how well these fruits perform in the presence of large mammals. 

Finally, for anyone familiar with Maclura, you will notice that the tree is armed with large spines. Why the heck does a large tree need to arm itself so extravagantly all the way to the top? Again, if you need things like mammoths or giant ground sloths to disperse your seeds, you may want to take some extra precautions to make sure they aren't snacking on you as well. It takes energy to produce spines so it is reasonable to assume that the tree would not go through so much trouble to protect even its crown if there once wasn't animals large enough to reach that high. The Pleistocene megafauna went extinct in what is evolutionarily speaking only the blink of an eye. Trees like the Osage orange have not had time to adapt accordingly. As such, without the helping hand of humans, this tree would still be hanging on to a mere fraction of its former range down in the Red River region of Texas.

Further Reading:
http://plants.usda.gov/core/profile?symbol=MAPO

http://www.americanforests.org/magazine/article/trees-that-miss-the-mammoths/

http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0001745