Setaria viridis aka Green Bristle Grass

Setaria viridis is a grass in the Poaceae family. Names include green foxtail, green bristlegrass, and rough bristle grass. Kew places its native range across the Old World into Australia. This includes central and southeastern parts of Australia. NC State describes it as native to Eurasia. It is not native to Britain or Ireland. NC State treats it as an annual. Kew records an annual or perennial life form.

The plant forms a dense clump with many spreading stems. NC State gives heights of 2–6 feet [0.61–1.83 metres]. Its listed spread is 1–2 feet [0.30–0.61 metres]. The smooth, round stems are green and lack scent. Their bases may lie along the ground before turning upward. Light green leaves grow in an alternate pattern. Each narrow blade has smooth edges and clear, fine veins. Leaves measure about 0.17–1 foot [0.05–0.30 metres] long. Their width reaches about 0.08 foot [0.025 metres]. The blades droop, with rough upper faces and mostly hairless undersides. Leaf sheaths may have purple bases and a few hairs.

Flowers appear in spring and summer, with bloom starting early. Each flower head is a dense, spike-like panicle. It measures about 0.08–0.33 foot [0.025–0.10 metres] long. The head stands upright but may bend at its tip. Small flower clusters, called spikelets, crowd along the panicle. Each has one to three green or purple bristles beneath it. The fruit is a caryopsis, the grain-like fruit of grasses. Its seed is oval, flattened, and tapered. Seeds drop from the spikelets and allow the plant to spread.

Green foxtail grows fast in full sun or partial shade. It accepts many soils, including clay, sand, and shallow rocky ground. It grows in moist soil and tolerates dry spells. Good drainage suits it. It favors poor soil in places where people disturb the ground. These include the disturbed sites noted by NC State. The supplied sources give no hardiness zone. Its fast growth does not make it low-maintenance in gardens. NC State rates its maintenance needs as high.

Its main landscape drawback is its strong tendency to become weedy. Seed production can yield several generations within one growing season. It spreads fast, though it enters good-quality natural areas less readily. NC State reports no major pest or disease concerns. Some small mammals and grazing animals eat the plant. The evidence does not establish food uses for people. It also gives no basis for a toxicity rating.