Musings of a New Naturalist: Amazing Awns

Hesperostipa [Stipa] comata richardsonii (Needle-and-thread grass) near Lyons, Colorado.Date5 July 2005, 07:18SourceOwn workAuthorCharles Sauer

Did you know some grasses use a trick to plant their seeds?

I didn’t know about this trick until a recent naturalist training out on a prairie, south of Boulder, CO. We came upon a thigh-high grass called Needle-and-thread Grass with wispy curled structures near the top. The curled structures are called awns; they are the threads. The awn attaches to a sharply pointed seed, the needle. Once the seed matures and disperses, aided by wind, the awn works its magic. Nightly humidity and rain soak into the awn and unfurl it, driving the seedhead into the soil. As the air and awn dry, the awn curls again, but tiny hairs on the awn prevent the seed from slipping back. More moisture unfurls the awn again and the cycle repeats, drilling the seed down into the soil.

Many other species of grasses and even flowers, such as sunflowers, use variously-shaped awls to catapult or bury their seeds, or to hitch a ride on the fur of a passing animal.

I had no idea grasses are so clever! I wonder whether awns inspired our sewing implements through biomimicry.

Below is a close-up of the awn.

Hesperostipa [Stipa] comata richardsonii (Needle-and-thread grass) seed. Found near Lyons, Colorado.

Charles Sauer - Own work

---