In the late 1940s a Swiss engineer was taking a nature walk with his dog when he noticed cockleburs sticking to his pants. The engineer was curious about these "sticky seeds" and took a closer look at them using a microscope. He found something that gripped him: the burs were covered with hooks that stuck in the fibers of his clothes. He was fascinated by this finding, began experimenting and, a few years later, he patented a product called Velcro®.
Why would cockleburs go for a ride on a Swiss engineer? If we want to go somewhere, we have lots of choices. We can walk, bike or go by car. Plants, if you'll pardon the pun, are more rooted. When a plant needs to move it has to do so vegetatively, such as when strawberry plants send out runners, or go by seed. The movement of a seed from its parent to another place is called seed dispersal.
There are many different types of "sticky seeds" in Missouri, some of which are seeds and others that are actually fruits. Some common ones are beggars' ticks, Spanish needles, tick trefoil, cheatgrass, needlegrass, burdock and cocklebur. Seeds of broad-leaved plantain are about as small as the head of a pin, while the fruits of cockleburs can be as wide as a nickel. The fruits of burdock are shaped like a top and others, such as beggars' ticks' fruits, are long and flat.
Whatever their shape, fruit and seed hitchhikers have one thing in common: they all can latch onto passing animals, including you and me. Sometimes, the fruits seem to leap out and attach themselves. And how the hitchhikers attach themselves is another story. Some use hooks or barbs while others use sticky fluids.
You can find sticky fruits and seeds throughout Missouri, from the prairies of the southwest and north to the forests and glades of the Ozarks, maybe even in your own backyard. Some of the common ones are in a group of plants called tick trefoils. Tick trefoils belong to the same family as the garden pea and string bean and have small purple to white, pealike flowers.
Some tick trefoils sprawl across the ground, while others grow waist-high or taller. A whole tick trefoil fruit looks like a flattened string bean pod with a narrow waist between each seed. Tick trefoil fruits are covered with hooked hairs. They grow in many types of places and start to produce sticky fruits early to mid-summer.
Burdock, which is in the same family as daisies and sunflowers, also has sticky fruits. Its tube-shaped purple flowers resemble a thistle. But burdock leaves are large and soft, while thistle leaves are jagged with sharp points on the edges. Burdock fruits are some of the largest in the state and are covered with stiff hooks that easily grab fur or clothing.
Burdocks are weeds that originally came from Europe and are a good example of how sticky fruits and seeds move across long distances. Maybe when cows or horses were shipped from Europe to America, some of the animals had burdocks stuck to them. When the animals arrived in the New World, a settler may have picked off the fruits and tossed them where they could grow.
In Missouri, burdocks mostly are found in places associated with humans, such as old fields, along roads and in vacant lots. They flower and make fruit from late summer until late into fall.
Agrimony belongs to the same family as the apple, but instead of bearing applelike fruits, it has a small, greenish to brown fruit. Agrimony can grow as tall as 6 feet or as short as 1 foot, but it generally grows to about waist height. Agrimony is another example of a fruit that uses hooks, and it is hard to remove. What a wonderful way for an agrimony fruit to go to market: get attached to a cow in a pasture and then be whisked away to a livestock market. And then, if lucky, germinate in a place that has lots of fertilizer and moisture.
Beggars' ticks, Spanish needles, tickseed sunflower and bur marigolds are all synonyms for a group of plants with sticky fruits that are related to sunflowers. They have bright yellow flowers and produce fruits that are long and flat with prongs. When those prongs work through your socks, they can make you want to scratch your ankles. Most of the beggars' ticks grow in damp areas in Missouri, such as low sites around streams, marshes or ditches.
Not all sticky seeds use hooks or prongs to get on board a passing animal. Like many other plants, the broad-leaved plantain has its seeds in a fruit. However, after the seeds mature, the fruit breaks open, and the seeds are released. When the seeds get wet, they become coated with a sticky, jellylike fluid. The fluid is sticky enough to attach the seed to a passing body. Broad-leaved plantains grow in fields, yards, gardens, moist woods and along railroads throughout Missouri.
It seems as if most any place you go in Missouri, you're likely to pick up a sticky seed or fruit. Most of them are easily removed (at least from your pants) by carefully scraping or picking them off with your fingers. Removing them from behind a dog's ears may be another matter.
As you remove your unwanted guests, stop and think for a moment about how you've moved these hitchhikers to a new place. Who knows, maybe this new spot has what it takes for that little seed to grow up to an adult plant.
Editor - Tom Cwynar
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