This section is from the book "Wayside And Woodland Blossoms", by Edward Step. Also available from Amazon: Wayside And Woodland Blossoms: A Guide To British Wild-Flowers.
We have three British species of Wild Oat, but a knowledge of their structure and differences may be best obtained perhaps by a consideration of the cultivated Oat of our fields. It is indeed probable that the cereal oat is but a cultivated form of our Common Wild Oat (A.fatua), for Professor Buckman succeeded years ago in obtaining as the ninth generation from seeds of A.fatua good crops of the farmers' varieties called White Tartarian and Potato Oats. It is known that oats shed in harvesting often degenerate into the wild forms. As a cereal the Oat does not appear to be nearly so ancient as wheat and barley, for it was not cultivated by the Hebrews, the Egyptians, Greeks or Romans.
The genus is distinguished by having its flowers in a lax-panicle, the spikelets borne principally upon long, slender stalks. Each spikelet contains two or more flowers, of which the upper one is usually imperfect, and each is armed with a long twisted and bent awn. There are two outer glumes, each flowering glume deeply notched, the awn arising from the bottom of the notch. The pale is two-nerved, the scales two-toothed, the stamens three. The ovary has a hairy top and two short styles with feathery stigmas. The fruit adheres to the glume.
I. Wild Oat (Avena fatua). An annual with two- or three flowered spikelets which droop at length. The empty glumes with nine nerves, flowering glumes covered with stiff hairs. Brown awn much bent, the lower half twisted. Leaves flat and roughish; sheaths smooth. Cornfields. June to August.
II. Narrow-leaved Oat (A. pratensis). Perennial; not to besought in the place indicated by pratensis, as it is a plant of the moor and dry pasture. Spikelets half erect, six flowered. Leaves flat, or edges rolled inwards, smooth, hard and rigid. Lower sheaths rough. Flowering glume, rough. Awn only slightly bent. June and July.
III. Downy Oat (A. pubescens). Perennial. Spikelets half erect, two-flowered. Leaves flatter than A. pratensis, downy; sheaths very downy. Awns wider apart. Dry pastures. June and July.
The name is the old Latin term for oats and reeds.
Avena sativa. - Gramineae. The front opens and discharges the pollen away from the stigma; but it falls where insects seeking the honeyed glands (using the ovary as a perch) will get it upon their forelegs, and so attach it to the stigmas of the next flower they visit.
It flowers in August and September. This is the only British species.