Mystery Plant: Grasses – most important plants of all | Culture | Summerville Journal Scene

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Mystery Plant: Grasses – most important plants of all

Published Tuesday, January 05, 2010 11:45 AM

Summerville Journal Scene ®

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Linda Lee/USC Herbarium

The fruit produced by a grass flower is what we call a “grain.”

It would not be exaggerating to say that grasses are the most important plants, in terms of human economy, in the world. For one thing, it turns out that every major civilization has depended upon one (or more) grass species as a major food source. Consider the far Eastern civilizations, based upon rice as a staple crop, the American civilizations employing corn (or “maize”), and the Middle East and Roman Empire, built upon wheat and barley. Members of this family have additionally supplied humans with animal feed, turf, housing materials, and starches, used for the production of sugar and alcohol. In a negative sense, many grasses are important as weeds, some of which are quite troublesome.

The grass family is very complex, and is broken down into a number of different divisions, or "tribes", based on certain characteristics. The flowers and grains are of primary importance in identifying grasses, and studying these small parts takes practice, and considerable patience, at least for most students. The flowers of grasses are quite small, and are clustered into small units called spikelets. Each spikelet may contain from one to many flowers, depending on the species. Small, dry bracts surround the flowers, and as you might expect, we botanists have designated specific and somewhat curious names to these bracts. We won’t bother with too much of this terminology here. Anyway, some of these various structures are commonly ornamented with short or long points. In many species, these little points are elongated into needle-like spines, or awns. The way in which these spikelets are carried on the grass plant varies widely from group to group, and is in part responsible for the way we designate the various tribes.

It’s also useful to remember that the fruit produced by a grass flower is what we call a “grain”, which is not a very technical term. A true grain is a hard, one-seeded fruit; true grains are only produced by members of the grass family. The tiny seed within a grain has its wall completely fused to the inner wall of the grain itself, which means that the seed never falls out of or emerges from the grain. A good example of a grain would be a kernel of corn. One kernel is itself a single fruit --not a seed. There is indeed a seed, but it is inside the kernel, fused around its margins to the inside of the kernel.

This week's Mystery Plant is indeed a grass, and each of its flowers produces three prominent, slender awns. These awns are effective in tangling themselves into an animal's fur, or someone's socks, as an effective means of dispersing the grain. This plant is a common annual species, native and widespread just about everywhere east of the Mississippi River. It likes dry, sandy fields or other open, vacant places, and is usually thought of as a good indicator of previous soil disturbance. This species has a large number of close relatives, and these various species aren’t always easy to tell apart.

[Answer: "Three-awn grass," Aristida oligantha]

John Nelson is the curator of the Herbarium at the University of South Carolina. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196.

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