(Image: Beth Jusino via Flickr)

Every day for the past two months, I’ve walked out my front door and come face to face with a tall spire of pink flowers. Foxglove, or as some know it, digitalis, may be a weed but they’re a pretty flower and I sometimes let them be. I might pay for this later, because they are enjoyed by bumble bees and as a result have no trouble with pollination. That spire has turned a tannish husk this month and each cupped flower has dried into a goblet brimming with tiny ochre seeds. Without my intervention, this spire will sway in the wind spilling seeds every which way.

Seeds are magical vessels of life and quite literally we’d not exist without them. Plants have evolved innumerable ways to spread them about too. This dispersal is vital to the way most plants inhabit that landscape, because while it can be temporarily good for a species to dominate a forest or prairie, growing en masse invites things like fungal pathogens and insect predation. We struggle with plants like Himalayan blackberries and Scotch broom because they have been brought to a place where they have no insects or disease to knock them back, no browsing animals that suppress their rampant nature. (This is a massively simplistic way for me to describe plant communities but as generalities go, it has some truth too.) But I digress. The point here is that plants need conveyances because unlike the organisms that rely deeply on them for sustenance, they are individually static beings.

This problem of getting seeds into a suitable location has been solved by plants time and time again and you can see the results all around Capitol Hill. I bet you can guess many of these solutions, but the fact that they even exist still blows my mind.

Broadly plants can disperse their seeds by: hitching a ride externally on an animal, using the wind to carry them, getting eaten and deposited later, being carried off to be hidden in a larder, bursting apart dramatically, riding waterways, or spreading merrily about like the foxglove or a poppy.

We are most familiar with enticing animals to carry seeds about, because it’s part of our everyday existence. Humans have both inadvertently and purposefully carried seeds around the world, and we enjoy eating fruit that is often laden with seeds that just need a ride through our digestive system to find their forever home. Birds are some of the best dispersers for fruiting plants, particularly in our urban spaces. Troublesome plants like holly, hawthorn, laurel, blackberry, and ivy continue to show up in green spaces after hitching a ride in avian digestive systems. Though we might not want to eat most of the fruits on that list (or be able to without getting sick), all the plants above have done a good job of making alluring fruit that surrounds one or many seeds. On the hill we see this exacerbated by the lack of native foods, animals take what they can get.

A constant frustration for me in my garden are cleavers. Even if you don’t know the plant’s name (or know it as catchweed bedstraw), you might recognize them as the sticky clambering weed with florets of leaves and tiny white flowers. Those flowers develop into little balls of velcro that are particularly good at latching onto animal hair or say, the socks of the weirdo who wears them with sandals. Many of us are very familiar with having seeds lodged in our socks or have had to comb burrs out of an animal’s hair, a hint that this method is not just the cleavers’ idea.  Cleavers may have their merits, they are a medicinal plant, but I have to admit I find them mostly an annoyance and trying to rid myself of patches feels like battling cotton candy with wet hands. What’s worse is that I just end up just spreading it more because despite my knowledge of their ways, cleavers might still be smarter than me.

(Image: Eric Jusino via Flickr)

Once I’ve given up battling weeds on a hot day, riding the wind sounds pretty nice, and many plants launch their future offspring far away with the breeze. Bigleaf maples are one of many plants that have samaras, winged seed bodies that helicopter away from the parent tree. If you have one near you and tend a garden, even a few yards away, you can attest to this ability and the fecundity of the tree in general. However if your seeds are small, you don’t need to be nearly as tall as a maple to catch air. Dandelion seeds simply float up in a gust or after being disturbed, individual seeds carried aloft by a gossamer parasol that can carry them across mountain ranges or large bodies of water.

Black cottonwoods may be able to ride air currents too, but their ability to ride waves in the ever changing river systems where they evolved has allowed them to be one of the most common trees in disturbed areas around the Hill. They are second only to the red alder, tossing hundreds of thousands of seeds with great abandon every year, often into adjacent waterways. Joining them are many riparian species, like birches and cattails that have extremely light seeds that slide along on the water surface to a new location. But my favorite example is of water lily seeds, which are larger and hold buoyancy long enough to drift off from their parent plant, but then sink to the bottom to root.

Arguably the most fun method of seed dispersal is ballochory, or dispersal by bursting apart to fling seeds away. This might not get seeds far, but it doesn’t require anything but time and maybe some heat to achieve. Many members of the pea family rely on this method, including scotch broom, part of the reason it grows in such impenetrable swathes where it’s been allowed to take hold. On a hot day you can even hear broom seeds popping. Others like bittercress, or as I grew up calling it, shotweed, require mechanical disturbance to send them flying. This member of the mustard family seems to taunt the gardener trying to clean up a garden bed — every time you start to pull up the plants you aren’t intending to grow, you send thirty more of them off into the soil at your feet.

These generalities about seeds don’t leave much room for the sheer complexity of how plants go about their lives. It’s not merely enough to disperse one’s seeds, they have to find a good place to bed down, get the right amount of moisture and nutrients, and avoid being eaten. Those acorns that squirrels haul off only make it sometimes, but clearly the system works, because oaks are widespread and diverse. I try to remember the tremendous work of evolution I witness every time I plant a seed or curse at those that have spread in a place I stupidly try to keep clear. Thankfully, and despite our best efforts, plants continue to find ways to spread their seeds and even when the actual results are a mixed bag, the world is a brighter and more beautiful place for their creative endurance.

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