A celebration of the ways seeds transport themselves around the world and onto our pants and pets.
Story and photos by Chris Helzer
We’ve all been there. You’re in the middle of a perfectly pleasant walk through a woodland, wetland or prairie and you glance down to find your pant legs covered with sticky seeds.
“Well, dadgum,” you exclaim, “would you look at that incredible seed dispersal adaptation!”
“Golly,” you continue, “those little hooked spines sure are effective at catching onto my pants. Ha! They’re on my socks, as well! I bet they work pretty great on dogs, too. Bowzer, come! Yep, look at that, they work spectacularly well on dogs!”
“Hey, Frank,” you call to your friend, “come over here and check out how sticky these little seeds are. It’s going to take me hours to get them all off my clothes. Aren’t they amazing?”
It’s hard not to admire the way some plants have figured out how to move their seeds around the world. Sure, it adds a few hours of work to your outdoor adventure, but when you put things in perspective, it’s a small price to pay for an intimate look at a natural wonder, right? Besides, what were you going to do with all that time, anyway?
There’s a good reason those seeds are so proficient at adhering to your socks. It’s part of a broader strategy for reproduction and territory expansion. When you brush up against a plant and come away with a scad of little marvels clinging to you, that plant is handing you responsibility for transporting its children to a new and safe location. I hope you take that responsibility seriously.
Plants create and release seeds as a way to help their kids move to exotic new locations. Unfortunately, most of those seeds never make it to full planthood. They get eaten or otherwise perish before they land in a spot where there is bare soil, sufficient light and moisture, and manageable competition from nearby plants. That’s OK. Only one seed has to be successful to perpetuate the genetic lineage of its parent.
Arguably, seeds have the best chance of becoming a plant near their parent. After all, if the parent is thriving, the site conditions must be pretty good, right? If the goal was simply to create successful progeny, plants might all just drop their seeds straight down, or maybe a few feet away. That approach, however, only works until a disease, burrowing badger, or other threat appears at that localized site and wipes everyone out. So much for that genetic lineage.
Creating seeds that travel gives plants a chance to set up satellite locations and hedge their bets a little. Hopefully, a little distance between parents and kids means one or the other will avoid that fungal infection or badger activity. Over many generations, a family line might spread across many acres, or even square miles, and really cement its legacy.
Seed dispersal, then, is a crucial strategy for most plants, and the ways plants move those seeds across the landscape can vary widely. Generally, though, most plants create seeds that can be carried by wind, be ingested and deposited by animals, or become attached to the hide of a passing creature.
The first of those approaches consists of making lightweight seeds with little feathery appendages that help them float away on a breeze to seek their fortune elsewhere. Plants can often create hundreds or thousands of those tiny wind-dispersed seeds per year, and while most still fall to the ground or get stuck in vegetation close to their parents, a few may travel many miles.
Wind dispersal sounds like a terrific strategy until you realize that to reduce weight, seeds can’t carry much food within their seed coat. That means they don’t have long to hit the soil and germinate before they die. They also have a thin seed coat, which means they are vulnerable to damage from temperature extremes, digestion by animals and other threats. As a result, the risk for an individual seed is extraordinarily high.
On the other end of that spectrum, there are plants that give their seeds heavy-duty protective coverings and try to attract animals to eat them. In most cases, those seed coats can protect the integrity of the seed as it passes through an animal’s digestive tract, and it can emerge and be deposited far away from where it was consumed. You might say those seeds are both heavy-duty and heavy-in-doody. You probably shouldn’t, though.
Making large seeds with robust seed coats, however, takes a lot of resources from a plant. That investment increases even more when a plant wraps its seed in a sweet, fleshy fruit to entice a robin or raccoon to make a meal out of it. As a result of that high cost, plants generally don’t make very many of those seeds. The few seeds they do create have a relatively high chance of surviving their journey, but there’s still a huge risk that none will be deposited where they can germinate and grow to adulthood.
Seeds that can hitchhike on animals (or human hikers) kind of split the difference between those other two strategies. They tend to be larger and more robust than wind-dispersed seeds, but the investment in their construction is much less than is needed to create a plum or raspberry. In most cases, the plant simply adds some spines, hooks or other similar appendages to the seed coat or seed pod. The variety found within those attachment features is incredible.
Hitchhiker seeds can latch onto a passing animal’s coat (or pants, as applicable) when that animal brushes up against them. They then get carried until they’re dislodged, either intentionally or unintentionally. Sometimes, there’s a very short period between attachment and detachment (“Ouch! What is that? Get it off me!”).
More often, the seed’s courier doesn’t realize it has passengers until it has moved a fair distance away. In fact, many seeds are brushed off before an animal even knows they were there — dislodged as the animal scrapes against other vegetation or rolls around in the dirt for a nice, pleasing dust bath.
There are lots of plants that equip their seeds with hooks, spines or other features that help them hitchhike on animals, including humans. Here are six plants that Nebraska outdoor enthusiasts are likely to encounter. Each has its own unique characteristics, worthy of your appreciation.
Needlegrasses (Hesperostipa sp) are perennial grasses that bloom in late May and early June across Nebraska. Two, in particular, have seeds that resemble long spears with sharp points. Needle-and-thread grows mostly in sandy soil and can be found throughout the northwestern two-thirds of the state.
Porcupine grass, which has even larger “spears,” is in the northeastern two-thirds of the state, meaning that in much of central Nebraska, you might find both.
The seeds of these needlegrasses are encased in the sharp “spear head,” which also features stiff hairs that help keep it from slipping back out of whatever it sticks into. That spear head is attached to a long awn, similar to a very thick hair, which acts as the spear’s shaft. As the seeds mature, they become loose in their moorings. If a furry animal or hiker brushes against them, those sharp points embed themselves in fur, clothing or even skin, held firmly in place by the aforementioned stiff hairs.
It’s easy to imagine this tactic being very effective when bison roamed most of Nebraska, covered in thick,curly hair. Of course, it’s also very effective on moisture-wicking wool socks and lightweight, breathable pants made with blends of nylon, polyester and spandex. Once needlegrass seeds become embedded, further jostling often pushes them further into whatever material they’re attached to until they eventually encounter the skin beneath. That’s usually when they’re detected, yanked out and discarded in a new location.
After needlegrass seeds are deposited in a new site, the long awn (the spear’s shaft) gets to display its additional ability. The awn can repeatedly coil up and straighten as humidity conditions fluctuate over a period of days. As a result, the seed can effectively drill itself through thatchy vegetation and right into the soil where it can germinate and grow.
Cocklebur (Xanthium strumarium) is a native annual broadleaf plant found across Nebraska that commonly grows in crop fields or along wet habitats, often in bare ground within dried up wetland basins or stream banks. Young cocklebur seedlings, which resemble those of annual sunflowers, can release toxins into the soil that can suppress the germination and growth of nearby plants. The plants themselves, including the burs, are toxic as well, so try to avoid the temptation to eat them.
Two seeds are contained within each of the oval-shaped burs produced by cocklebur plants in the late summer or fall. Those burs contain hooked spines that effectively latch onto fur or fabric. Typically, those burs are relatively easy to detach from pants and socks but can be much more intractable in longer fur or hair.
Sandbur (Cenchrus longispinus) is a native annual grass that grows statewide in dry habitats and, like cocklebur, produces seeds inside sharp-pointed burs. It doesn’t compete well with most perennial plants, so it is often found in areas of sparse vegetation, or along the edges of trails and roads. Conveniently, of course, that’s where people and animals are likely to brush up against them. Sandburs are native in North America, but we have managed to export them to Europe, Australia and New Zealand, where they are appreciated about as much as they are here.
The burs of sandbur contain one to three seeds. Each bur features robust spines that point in every direction and easily penetrate clothing or skin. During the late summer and early fall, the burs are strategically located at ankle height, where pant legs, socks and boot laces can interact with them.
Beggarticks, aka beggar-ticks, beggar’s ticks or (obviously) Spanish needles, are all names given to a group of annual broadleaf plants in the genus Bidens. Most are found in wet habitats, where some produce showy sunflower-like blossoms and others don’t. They are annual plants that often occur where water level fluctuations or something else prevents perennial plants from being strongly established.
The seeds of beggarticks plants are encased within an elongated, hardened fruit with barbed awns at one end. Those awns make the fruits look like multi-tined spearfishing spear heads. They are certainly effective at spearing clothing, but they can also tangle themselves up in fur or hair.
Tickclover, aka tick-trefoil (Desmodium sp.) plants are perennial legumes with three-part leaves found in both prairies and woodlands. Many of the grassland species have beautiful flowers that attract lots of pollinating insects, and the leaves and stems of younger plants are highly sought out by grazing cattle. Except for showy tickclover (Desmodium canadensis), which is statewide, most species are restricted to the eastern one-third of Nebraska.
The fruits of tickclover plants are called “loments” and are covered with tiny hooked hairs. They weren’t, as far as I can tell, but they could have been the inspiration for Velcro® because they work the same way. They adhere so well to most shirt and pants fabric, and especially to socks, that they can usually survive a trip through the laundry, much to the frustration of people hoping for an easy way to get rid of them. Each loment is like an envelope that contains a single very hard-coated seed.
Virginia Stickseed (Hackellia virginiana) is a short-lived, biennial forb with small flowers. It is the most common of the three Hackellia species in Nebraska and is found mostly in the eastern half of the state, but also in places in the northwest. Stickseed grows in wooded areas, including right along the edges where a dog or human child might easily encounter them without having to work very hard.
The fruits of stickseed are called “nutlets,” which sound fun, and are found in clusters of four along the long flowering stems of the plant. The nutlets are covered with little barbed prickles that are extraordinarily good at sticking to clothing and fur.
Prickle, by the way, is a technical botanical term that also refers to the spiny parts of rose stems. Fortunately, the prickles on stickseed nutlets are small enough that they aren’t painful to the touch of anyone trying to scrape them off of pants or gently pry them from the fur of a dog.
Because most of us aren’t botanists, the commonly-used names of many of these sticky-seeded plants are used interchangeably. As a result, when you post a selfie showing off a particularly nice spread of stickseed nutlets on your pant leg, some of your friends might use names like beggar’s-lice, beggar-ticks or sticktight in their comments. That’s OK. The important thing is to celebrate the effectiveness of the seed dispersal strategies of these plants, regardless of what you call them.
Even as you revel in the amazing adaptations of these sticky seeds, however, you will probably want to remove them from your clothing or pets. There is no single best way to do this. In some cases, a comb can help remove cockleburs or sandburs from clothing without getting your fingers poked by the sharp spines. If you have to use your fingers, many people recommend wetting your fingers first to make the process less painful. I’m not sure why that works.
In other cases, you’ll probably have to come up with your own innovative tactics for seed removal. Otherwise, the standard method is to simply pry them off one at a time while humming a little tune to yourself to make the time pass pleasantly. Try to avoid more drastic measures such as shaving your dog, burning your clothes or using foul language.
Most importantly, take time to marvel at the various and inventive ways these plants have found to transport their potential offspring to new locales. Don’t whine about those spines. Don’t be a cur about those burs. Celebrate your moments with those loments and admire the stick-to-it-ness of the seeds that have chosen you to help them travel the world.