Ground Beetles as Weed Seed Predators

As diurnal animals, we are generally unaware of the slew of animal activity that occurs during the night. Even if we were to venture out in the dark, we still wouldn’t be able to detect much. Our eyes don’t see well in the dark, and shining a bright light to see what’s going on results in chasing away those creatures that prefer darkness. We just have to trust that their out there, and in the case of ground beetles, if they’re present in our gardens we should consider ourselves lucky.

Ground beetles are in the family Carabidae and are one of the largest groups of beetles in the world with species numbering in the tens of thousands. They are largely nocturnal, so even though they are diverse and relatively abundant, we rarely get to see them. Look under a rock or log during the day, and you might see a few scurry away. Or, if you have outdoor container plants, there may be a few of them hiding out under your pots with the pillbugs. At night, they leave the comfort of their hiding places and go out on the hunt, chasing down grasshoppers, caterpillars, beetle grubs, and other arthropods, as well as slugs and snails. Much of their prey consists of common garden pests, making them an excellent form of biological control. And, as if that weren’t enough, some ground beetles also eat the seeds of common weeds.

Harpalus affinis via wikimedia commons

Depending on the species, a single ground beetle can consume around a dozen seeds per night. In general, they prefer the seeds of grasses, lambsquarters (Chenopodium album), pigweeds (Amaranthus spp.), and various plants in the mustard family (Brassicaceae). The seeds of these species are small with seed coats that are easily crushed by a beetle’s mandibles. Providing suitable habitat, avoiding insecticides, and minimizing soil disturbance (i.e. reducing or eliminating tillage) are ways that healthy ground beetle populations can be encouraged and maintained. Ground beetles prefer dense vegetation where they can hide during the daytime. Strips of bunchgrasses and herbaceous perennials planted on slightly raised bed (referred to as beetle banks) are ideal because they provide good cover and keep water from puddling up in the beetles’ hiding spots.

The freshness of weed seeds and the time of year they are available may be determining factors in whether or not ground beetles will help control weed populations. A study published in Weed Science (2014), looked at the seed preferences of Harpalus pensylvanicus, a common species of ground beetle that occurs across North America. When given the choice between year old seeds and freshly fallen seeds of giant foxtail (Setaria faberi), the beetles preferred the fresh ones. The study also found that when giant foxtail was shedding the majority of its seeds, the density of beetles was on the decline, meaning that, at least in this particular study, most of the seeds would go uneaten since fewer beetles were around when the majority of the seeds were made available. Creating habitat that extends the ground beetles’ stay is important if the goal is to maximize the number of weed seeds consumed.

Harpalus pensylvanica via wikimedia commons

Of course, the seeds of all weed species are not considered equal when it comes to ground beetle predation. Several studies have sought to determine which species ground beetles prefer, offering seeds of a variety of weeds in both laboratory and field settings and seeing what the beetles go for. Pinning this down is difficult though because there are numerous species of ground beetles, all varying in size and activity. Their abundances vary from year to year and throughout the year, as do their food sources. Since most of them are generalists, they will feed on what is available at the time. A study published in European Journal of Entomology (2003) found a correlation between seed size and body mass – small beetles were consuming small seeds and large beetles were consuming large seeds, relatively speaking.

Another study published in European Journal of Entomology (2014) compared the preferences of ground beetles in the laboratory to those in the field and found that, in both instances, the seeds of field pansy (Viola arvensis) and shepherd’s purse (Capsella bursa-pastoris) were the preferred choice. The authors note that both species have lipid-rich seeds (or high “energy content”). Might that be a reason for their preference? Or maybe it’s simply a matter of availability and “the history of individual predators and [their] previous encounters with weed seed.” After all, V. arvensis was “the most abundant seed available on the soil surface” in this particular study.

Pterostichus melanarius via wikimedia commons

A study published in PLOS One (2017), looked at the role that scent might play in seed selection by ground beetles. Three species of beetles were offered the seeds of three different weed species in the mustard family. The seeds of Brassica napus were preferred over the other two by all three beetle species. The beetles were also offered both imbibed and non-imbibed seeds of all three plants. Imbibed simply means that the seeds have taken in water, which “can result in the release of volatile compounds such as ethanol and acetaldehyde.” The researchers wondered if the odors emitted from the imbibed seeds would “affect seed discovery and ultimately, seed consumption.” This seemed to be the case as all three beetle species exhibited a preference for the imbibed seeds.

Clearly, ground beetles are fascinating study subjects, and there is still so much to learn about them and their eating habits. If indeed their presence is limiting the spread of weeds and reducing weed populations, they should be happily invited into our farms and gardens and efforts should be made to provide them with quality habitat. For a bit more about ground beetles, check out this episode of Boise Biophilia.

Further Reading:

Camel Crickets and the Dust Seeds of Parasitic Plants

A common way for plants to disperse their seeds is to entice animals to eat their seed-bearing fruits – a strategy known as endozoochory. Undigested seeds have the potential to travel long distances in the belly of an animal, and when they are finally deposited, a bit of fertilizer joins them. Discussions surrounding this method of seed dispersal usually have birds and mammals playing the starring roles – vertebrates, in other words. But what about invertebrates like insects? Do they have a role to play in transporting seeds within themselves?

Certain insects are absolutely important in the dispersal of seeds, particularly ants. But ants aren’t known to eat fruits and then poop out seeds. Instead they carry seeds to new locations, and some of these seeds go on to grow into new plants. In certain cases there is an elaisome attached to the seed, which is a nutritious treat that ants are particularly interested in eating. Elaisomes or arils have also been known to attract other insects like wasps and crickets, which may then become agents of seed dispersal. But endozoochory in insects, at first, seems unlikely. How would seeds survive not being crushed by an insect’s mandibles or otherwise destroyed in the digestion process?

camel crickets eating fruits of parasitic plants (via New Phytologist)

While observing parasitic plants in Japan, Kenji Suetsugu wanted to know how their seeds were dispersed. Many parasitic plants rely on wind dispersal, thus their seeds are minuscule, dust-like, and often winged. However, the seeds of the plants Suetsugu was observing, while tiny, were housed in fleshy fruits that don’t split open when ripe (i.e. indehiscent). This isn’t particularly unusual as other species of parasitic plants are known to have similar fruits, and Suetsugu was aware of studies that found rodents to be potential seed disperers for one species, birds to be dispersers of another, and even one instance of beetle endozoochory in a parasitic plant with fleshy, indehiscent fruit. With this in mind, he set out to identify the seed dispersers in his study.

Suetsugu observed three achlorophyllous, holoparisitic plants – Yoania amagiensis, Monotropastrum humile, and Phacellanthus tubiflorus. While their lifestyles are similar, they are not at all closely related and represent three different families (Orchidaceae,  Ericaceae, and Orobanchaceae respectively). All of these plants grow very low to the ground in deep shade below the canopy of trees. Air movement is at a minimum at their level, so seed dispersal by wind is not likely to be very effective. Using remote cameras, Suetsugu captured dozens of hours of footage and found camel crickets and ground beetles to be the main consumers of the fruits, with camel crickets being “the most voracious of the invertebrates.” This lead to the next question – did the feces of the fruit-eating camel crickets and ground beetles contain viable seeds?

Monotropastrum humile via wikimedia commons

After collecting a number of fecal pellets from the insects, Suetsugu determined that the seeds of all three species were “not robust enough to withstand mastication by the mandibles of the ground beetles.” On the other hand, the seeds passed through the camel crickets unscathed. A seed viability test confirmed that they were viable. Camel crickets were dispersing intact seeds of all three parasitic plants via their poop. The minuscule size of the seeds as well as their tough seed coat (compared to wind dispersed seeds of similar species) allowed for safe passage through the digestive system of this common ground insect.

In a later study, Suetsugu observed another mycoheterotrophic orchid, Yoania japonica, and also found camel crickets to be a common consumer of its fleshy, indehiscent fruits. Viable seeds were again found in the insect’s frass and were observed germinating in their natural habitat. Seutsugu noted that all of the fruits in his studies consumed by camel crickets are white or translucent, easily accessible to ground dwelling insects, and give off a fermented scent to which insects like camel crickets are known to be attracted. Camel crickets also spend their time foraging in areas suitable for the growth of these plants. All of this suggests co-evolutionary adaptations that have led to camel cricket-mediated seed dispersal.

Yoania japonica via wikimedia commons

Insect endozoochory may be an uncommon phenomenon, but perhaps it’s not as rare as we once presumed. As mentioned above, an instance of endozoochory by a beetle has been reported, as has one by a species of cockroach. Certainly the most well known example involves the wetas of New Zealand, which are large, flightless insects in the same order as grasshoppers and crickets and sometimes referred to as “invertebrate mice.” New Zealand lacks native ground-dwelling mammals, and wetas appear to have taken on the seed dispersal role that such mammals often play.

Where seeds are small enough and seed coats tough enough, insects have the potential to be agents of seed dispersal via ingestion. Further investigation will reveal additional instances where this is the case. Of course, effective seed dispersal means seeds must ultimately find themselves in locations suitable for germination in numbers that maintain healthy populations, which for the dust seeds of parasitic plants is quite specific since they require a host organism to root into. Thus, effective seed dispersal in these scenarios is also worth a more detailed look.

Further Reading:

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For more stories of seed dispersal check out the first issue of my new zine, Dispersal Stories.

2019: Year in Review

It’s the start of a new decade and the beginning of another year of Awkward Botany. As we’ve done in years prior, it’s time to look back at what we’ve been up to this past year and look forward to what’s coming in the year ahead. Thank you for sticking with us as we head into our eighth year exploring and celebrating the world of plants.

The most exciting news of 2019 (as far as Awkward Botany is concerned) is the release of the first issue of our new zine, Dispersal Stories. It’s a compilation of (updated) writing that originally appeared on Awkward Botany about seeds and seed dispersal and is the start of what I hope will be a larger project exploring the ways in which plants get around. Look forward to the second issue coming to a mailbox near you sometime in 2020.

Also new to our Etsy Shop is a sticker reminding us to always be botanizing, including while riding a bike. Stay safe out there, but also take a look at all the plants while you’re cruising around on your bike or some other human-powered, wheeled vehicle. Whether you’re in a natural area or out on the streets in an urban or rural setting, there are nearly always plants around worth getting to know.

This year we also started a Ko-fi page, which gives readers another avenue to follow us and support what we do. Check us out there if Ko-fi is your thing.

Buy Me a Coffee at ko-fi.com

We also still have our donorbox page for those who would like to support us monetarily. As always you can stay in touch with us by liking and following our various social media accounts (Facebook, Twitter, Tumblr, and our currently inactive, but that could change at any moment Instagram). Sharing is caring, so please be sure to tell your friends about Awkward Botany in whatever way you choose. We are always thrilled when you do.

Below are 2019 posts that are part of new and ongoing series. You can access all other posts via the Archives widget. 2019 saw a significant drop in guest posts, so if you’d like to submit a post for consideration, please visit our Contact page and let me know what you’d like to write about. Guest writers don’t receive much in return but my praise and adulation, but if that sounds like reward enough to you, then writing something for Awkward Botany might just be your thing. And while we’re on the topic of guest posts, check out this post I wrote recently for Wisconsin Fast Plants.

Happy Reading and Plant Hunting in 2020!

Inside of a Seed & Seed Oddities:

Podcast Review:

Poisonous Plants:

Tiny Plants:

Eating Weeds:

Using Weeds:

Drought Tolerant Plants:

Tea Time:

Field Trip:

Awkward Botanical Sketches:

Guest Posts:

Out Now! Dispersal Stories #1

Before I started this blog, I had spent 16 years publishing zines at a steady clip and sending them to all corners of the world through the mail. I had never really meant to abandon zines altogether, and in some ways, putting all my writing efforts into a blog felt a little like a betrayal. My intention had always been to one day put together another zine. Now, six and a half years later, I’m happy to report that day has come.

Rather than bring an old zine back from the grave, I decided to make a new zine. Thus, Dispersal Stories #1. It’s quite a bit different from zines I’ve made in the past, which were generally more personal and, I guess, ranty. In fact, Dispersal Stories is very much like this blog, largely because it is mostly made up of writing that originally appeared here, but also because its main focus (for now) is plants. What sets it apart is that, unlike this blog, it zeroes in on a specific aspect of plants. As the title suggests, it’s all about dispersal. For much of their life, plants are essentially sessile. Once they are rooted in place, they rarely go anywhere else. But as seeds, spores, or some other sort of propagule they are actually able to move around quite a bit. The world is their oyster. What’s happening during this period of their lives is the focus of Dispersal Stories.

But why do a zine about this? Apart from just wanting to do another zine after all these years, my hope is that Dispersal Stories will be the start of a much more ambitious project. A book perhaps. My interest in dispersal was born out of my interest in weeds, and there is so much that I would like to learn and share about both of these subjects – so much so that the blog just doesn’t really cut it. So, I’m expanding the Awkward Botany empire. First a zine, then a book, then … who knows? I’m an oyster! (Or something like that.)

Dispersal Stories #1 is available in our etsy shop, or you can contact me here and we can work something out. While you’re at it, check out our new sticker.

If you love looking at plants and learning their names, then you probably enjoy doing it any chance you get. Usually it’s an activity you do while walking, but who says you can’t botanize while riding a bike? This sticker is inspired by a friend who once said that while mountain biking you get to “see three times as many flowers in half the time!” Stick it on your bike or in some other prominent location to remind yourself and others that we can botanize anytime anywhere.

Your purchase of one or both of these items helps support what we do. You can also support us by buying us a ko-fi or putting money in our donorbox. Sharing these posts also helps us out. If you get a copy of the zine, let us know what you think by sending us an email, a message on twitter or facebook, or by leaving a comment below. As always, thanks for reading.

Related Posts:

Pine Cones Are Like Hangars for Pine Tree Seeds

Over the past year I’ve written about the making of pine tar and the drinking of pine needle tea. But why stop there? Pines are a fascinating group of plants, worthy of myriad more posts, and so my exploration into the genus continues with pine cones and the seeds they bear.

Pines are conifers and, more broadly, gymnosperms. They are distinct from angiosperms (i.e. flowering plants), with the most obvious distinction being that they don’t make flowers. Since they are flowerless, they are also fruitless, as fruits are seed-bearing structures formed from the ovary or ovaries of flowering plants. Pines do make seeds though, and, as in angiosperms, pollen is transported from a “male” organ to a “female” organ in order for seeds to form. Rather than being housed in a fruit, the seeds are essentially left out in the open, which is why the term “naked seeds” is frequently used in reference to gymnosperms.

seed cone of Scots pine (Pinus sylvestris ‘Glauca Nana’)

In the case of pines and other conifers, the seeds may be naked, but they’re not necessarily homeless. They have the protection of cones, which is where the female reproductive organs are located. Male, pollen cones are separate structures and are smaller and less persistent than the cones that house the seeds. A cone, also known as a strobilus, is a modified branch. A series of scales grow in a spiral formation along the length of the branch, giving the cone its shape. On the inside of these scales is where the seeds form, two per scale. First they are egg cells, and then, after pollination and a period of maturation, they become seeds. The scales protect them throughout the process and then release them when the time is right.

With more than 120 species in the genus Pinus, there is great diversity in the size, shape, and appearance of pine cones. While at first glance they don’t appear all that different from one another, the cones of each species have unique characteristics that can help one identify the pine they fell from without ever having to see the tree. Pine cones are also distinct from the cones of other conifers. For one, pine cones take at least two or, in some cases, three years to reach maturity, whereas the cones of other conifers develop viable seeds in a single year. Pine cones are also known to remain on the tree for several years even after the seeds are mature – in some species up to 10 years or more – and they don’t always part with their seeds easily. Lodgepole pines (Pinus contorta) require high temperatures to melt the resin that holds their scales closed, the cones of jack pine (P. banksiana) generally only open in the presence of fire, and the seeds of whitebark pine (P. albicaulis) are extracted with the aid of birds (like Clark’s nutcracker) and other animals.

immature seed cone of lodgepole pine (Pinus contorta)

Every pine cone is special in its own right, but some stand out in particular. The largest and heaviest pine cones are found on Coulter pine (P. coulteri), measuring up to 15 inches long and weighing as much as 11 pounds with scales that come to a sharp point. It’s understandable why the falling cones of this species are frequently referred to as widowmakers. Longer cones, but perhaps less dangerous, are found on sugar pine (P. lambertiana). The tallest trees in the genus, the cones of sugar pine consistently reach 10 to 20 inches long and sometimes longer.

Pine tree seeds are a food source for numerous animals, including humans. Most are so small they aren’t worth bothering with, however, several species have seeds that are quite large and worth harvesting. Most commercially grown pine nuts come from stone pine (P. pinea) and Korean pine (P. koraiensis). In North America, a wild source for pine nuts is found in the pinyon pines, which have a long history of being harvested and eaten by humans.

immature seed cone of ponderosa pine (Pinus ponderosa)

The seeds of many pines come equipped with little wings called samaras, which aid them in their dispersal. Upon maturity, pine cone scales open and release the seeds. Like little airplanes leaving the hangar, the seeds take flight. Wind dispersal is not an effective means of dispersal for all pines though. A study published in Oikos found that seeds weighing more than 90 milligrams are not dispersed as well by wind as lighter seeds are. When it comes to long distance dispersal, heavier seeds are more dependent on animals like birds and rodents, and some pines rely exclusively on their services. The author of the study, Craig Benkman, notes that “bird-dispersed pines have proportionately thinner seed coats than wind-dispersed pines,” which he points out in reference to Japanese stone pine (P. pumila) and limber pine (P. flexilis), whose seeds weigh around 90 milligrams yet rely mostly on birds for dispersal. Benkman suspects that the seeds of these two species “would probably weigh over 100 milligrams if they had seed coats of comparable thickness as wind-dispersed seeds.”

Whitebark pine, as mentioned above, holds tightly to its seeds. Hungry animals must pry them out, which they do. Pine seeds are highly nutritious and supplement the diets of a wide range of wildlife. Some of the animals that eat the seeds also cache them for later. Clark’s nutcrackers are particularly diligent hoarders, harvesting thousands more seeds than they can possibly consume and depositing them in small numbers in locations suitable for sprouting.

Even large seeds that naturally fall from their cones have a chance to be dispersed further. As the seeds become concentrated at the base of the tree, ground-foraging rodents gather them up and cache them in another location, which Benkman refers to as secondary seed dispersal.

Particularly in pine species with wind dispersed seeds, what the weather is like helps determine when the hangar door will open to release the flying seeds. When it is wet and rainy, the scales of pine cones close up. The seeds wouldn’t get very far in the rain anyway, so why bother? When warm, dry conditions return, the scales open back up and the seeds are free to fly again. You can even watch this in action in the comfort of your own home by following the instructions layed out in this “seasonal science project.”

immature seed cones of limber pine (Pinus flexilis)

mature seed cones of limber pine (Pinus flexilis)

Further Reading:

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Photos of pine cones were taken at Idaho Botanical Garden in Boise, Idaho

Seed Dispersal by Way of Tree Climbing Goats

Goats are surprisingly good climbers. Given the opportunity, they’ll climb just about anything, including each other. So what’s stopping them from climbing a tree, especially if there is something up there they can eat? And so they do. Tree climbing goats are such a fascinating sight, they even have their own calendar. But the story doesn’t end there. The goats find food in the trees, entertaining humans as they go; meanwhile, the trees have a reliable partner in the goats, who inadvertently help disperse the tree’s seeds.

In general, goats don’t need to climb trees to find food. Goats aren’t known to be picky eaters, and there is usually plenty for them to eat at ground level. However, in arid climates where food can become limited, ascending trees to eat foliage and fruits is a matter of survival. This is the case in southwestern Morocco, where goats can be found in the tops of argan trees every autumn gorging on the fruits of this desert tree.

goats in Argania spinosa via wikimedia commons

Argan (Argania spinosa) is a relatively short tree with a sprawling canopy and thorny branches. It is the only species in its genus and is endemic to parts of Morocco and neighboring Algeria. The tree is economically important to the area due to the oil-rich seeds found within its bitter fruits. Argan oil has a variety of culinary uses and is also used medicinally and in cosmetics. To get to the oil, goats are often employed in harvesting the fruits. The goats retrieve the fruits from the tops of the trees and consume their fleshy outer layer. The hard, seed-containing pits are expelled, collected, and cracked open to get to the seeds.

This is where a team of researchers from Europe come in. There has been some confusion as to how the pits are expelled, with some reports claiming that they pass through the goats digestive track and are deposited in their manure. This is a common way for the seeds of many other plant species to be dispersed, and is carried out not only by goats and other ruminants, but also by a wide variety of mammals, as well as birds and even reptiles. However, considering the average size of the pits (22 mm long x 15 mm wide), the researchers thought this to be unlikely.

fruits of Argania spinosa via wikimedia commons

Others reported that the seeds were spat out in the goats’ cud while they ruminated. Goats, like other ruminants, have stomachs composed of multiple compartments, the first of which being the rumen. Partially digested food, known as cud, is sent back into the mouth from the rumen for further chewing and may be spat out or swallowed again. Goats are known to ruminate in the same location that they defecate, which results in confusion as to when and how certain seeds, like those of the argan tree, are deposited.

By feeding various fruits to a group of goats, the researchers were able to test the hypothesis that seeds could be regurgitated and spat from the cud and that this is a viable method of seed dispersal. The researchers reported that larger seeds were more commonly spat out than smaller seeds, but that “almost any seed could be ejected during, mastication, spat from the cud, digested, or defecated.” The viability of spat out seeds was tested, and over 70% of them were found to be viable.

pits and seeds of Argania spinosa via wikimedia commons

This discovery suggests that seed dispersal via spitting by ruminants could be a common occurrence – possibly far more common than previously considered. The researchers postulate that studies that have only considered seeds dispersed in manure “may have underestimated an important fraction of the total number of dispersed seeds” and that the seeds spat from the cud likely represent different species from those commonly dispersed in dung. In addition, the seeds of some species don’t survive the digestive tract of ruminants, so “spitting from the cud may represent their only, or at least their main, dispersal mechanism.”

This study surrounding the argan trees was followed up by the same group of researchers with a literature review that was published last month. The review looked into all available studies that mentioned seed dispersal via regurgitation by ruminants. While they considered over 1000 papers, only 40 published studies were found to be relevant for the review. From these studies, they determined that the seeds of 48 plant species (representing 21 different families) are dispersed by being spat from a ruminant’s cud, and that most of these plant species are trees and shrubs whose fruits contain large seeds. Also of note is that ruminants across the globe are doing this – representatives from 18 different genera were mentioned in the studies.

ruminating goat via wikimedia commons

The researchers conclude that this is a “neglected” mechanism of seed dispersal. It’s difficult to observe, and in many cases it hasn’t even been considered. Like so many other animals, ruminants can disperse seeds in a variety of ways. Seeds can attach to their fur and be transported wherever they go. They can pass through their digestive track and end up in their dung, potentially far from where they were first consumed. And, as presented here, they can be spat out during rumination. Investigations involving all of these mechanisms and the different plant species involved will allow us to see, in a much clearer way, the role that ruminants play in the dispersal of seeds.

The Flight of the Dandelion

The common dandelion (Taraxacum officinale) comes with a collection of traits that make it a very successful weed. Nearly everything about it screams success, from its asexually produced seeds to its ability to resprout from a root fragment. Evolution has been kind to this plant, and up until the recent chemical warfare we’ve subjected it to, humans have treated it pretty well too (both intentionally and unintentionally).

One feature that has served the dandelion particularly well is its wind-dispersed seeds. Dandelions have a highly-evolved pappus – a parachute-like bristle of hairs attached to its fruit by a thin stalk. The slightest breath or puff of wind will send this apparatus flying. Once airborne, a dandelion’s seed can travel up to a kilometer or more away from its mother plant, thereby expanding its territory with ease.

Such a low-growing plant achieving this kind of distance is impressive. Even more impressive is that it manages to do this with a pappus that is 90% empty space. Would you leap from a plane with only 10% of a parachute?

Dandelion flight was investigated by researchers at the University of Edinburgh, who used a wind tunnel along with long-exposure photography and high-speed imaging to observe the floating pappus. Their research was presented in a letter published in an issue of Nature in October 2018. Upon close examination, they observed a stable air bubble floating above the pappus as it flew. This ring-shaped air bubble – or vortex – which is unattached to the pappus is known as a separated vortex ring. While this type of vortex ring had been considered theoretically, this marked the first time one had been observed in nature.

Seeing this type of air bubble associated with the dandelion’s pappus intrigued the researchers. About a 100 filaments make up the parachute portion of the pappus. They are arranged around the stalk, leaving heaps of blank space in between. The air bubble observed was not what was expected for such a porous object. However, the researchers found that the filaments were interacting with each other in flight, reducing the porosity of the pappus. In their words, “Neighboring filaments interact strongly with one another because of the thick boundary layer around each filament, which causes a considerable reduction in air flow through the pappus.”

The pappus acts as a circular disk even though it is not one, and its limited porosity allows just enough air movement through the filaments that it maintains this unique vortex. “This suggests,” the researchers write, “that evolution has tuned the pappus porosity to eliminate vortex shedding as the seed flies.” Fine-tuned porosity and the resultant unattached air bubble stabilizes the floating fruit “into an equilibrium orientation that minimizes [its] terminal velocity, allowing [it] to make maximal use of updrafts.” The result is stable, long distance flight.

Wind-dispersed seeds come in two main forms: winged and plumed. Winged seeds are common in trees and large shrubs. They benefit from the height of the tree which allows them to attain stable flight. While such seeds have the ability to travel long distances, their success is limited on shorter plants. In this case, plumed seeds, like those of the dandelion, are the way to go. As the researchers demonstrated, successful flight can be achieved by bristles in place of wings. The tiny seeds of dandelions seen floating by on a summer breeze are not tumbling through the air haphazardly; rather, they are flying steadily, on their way to spoil the dreams of a perfect lawn.

Further Reading (and Watching):