Phoresy — Hitchin’ a Ride

Here’s a new word for your Thanksgiving dinner table — phoresy.  It’s a term describing the passive transport of one organism by another — thus, “hitchin a ride”.  While out in the backyard today I was reminded of how many ways plants use animals to disperse their seed for them, as I was continually having to pick the “cling-ons” off.

These are the mature seed pods of the Common Burdock plant, a bane to long-haired dogs, and hikers wearing fleece.  The spiny hooks on the exterior of the pod catch on everything, and the pods are extremely easily dislodged from the plant as you casually brush by them.  So imagine trying to walk through the scene below, without getting attacked by the Burdock.  This is where deer trails come in very handy.

Burdock is a biennial thistle.  It is recognizable in the spring by its huge curled leaves that lie close to the ground.  Later in the summer, the second year plant  bears a head of purple globular flowers, and in the fall, these demonish seed pods appear.  They generally hang down from the stem, the better to catch on to passers-by.

The spines on the seed pod might have been the inspiration for velcro, which also uses a hook and loop mechanism to stick two pieces of something together.

To better visualize the hooks…

The taproot of Burdock may reach 1 meter down into the soil and may be 1-2 cm thick.  This is the part of the plant for which humans have found a use — they shave the root, steep it in hot water, and make a “delightfully refreshing tea”.  Right.

Goldenrod also uses phoresy to disperse its seed in the fall.  The seed heads look soft and fluffy, like cottonwood down.  The seeds are loosely attached to the stem, with downy hairs that help them float in the air.

But a close encounter with the plant as one wades through the brush can deposit a whole lot of seed quickly.  That’s my collection of goldenrod seed on my blue fleece.

If you’re like our family and need to take a long walk after that big Thanksgiving dinner, watch out for the free riders that may be using you for transport (phoresy).




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