Vulpia myuros, the annual fescue, or rat's-tail fescue, is an annual grass species of the genus Vulpia. It was probably originally native to Eurasia, but it can now be found nearly worldwide as a naturalized species.
In the United Kingdom it forms dense, even swards of fine, hair-like stems in recently disturbed habitats, such as 3-10-year-old pulverised fuel ash. It is typically displaced by perennial grasses after about a decade.
Vulpia myuros is considered a noxious weed and invasive species in places where it is not native, especially in areas with a Mediterranean climate. For example, it is widespread in California, where it is now a dominant species in many types of grassy habitat.
Culms erect or geniculately ascending, 20–70 cm tall, 3–4-noded, smooth. Leaf sheaths loosely overlapping, shorter or lower longer than internodes, smooth, glabrous; leaf blades involute, 7–11 cm × 1–2 mm, adaxial surface pubescent, abaxial surface smooth; ligule 0.2–0.5 mm, truncate. Panicle linear, 10–20 × 0.5–1 cm, loose to somewhat dense, mostly curved or nodding, base enclosed by uppermost leaf sheath or just exserted from it. Spikelets oblong or wedge-shaped, 8–10 mm (excluding awns), florets 4–7; lower glume minute, 1–3 mm, upper glume linear-lanceolate, 3–8 mm, apex acute; lemmas 5–7 mm, back scabrid, 5-veined, margins scabrid or ciliolate, apex acuminate; awn 1.3–1.8 cm. Stamen 1; anther 0.4–1 mm. Caryopsis reddish brown, ca. 4 mm. Fl. and fr. Apr–Jul. 2n = 42.
Mountain slopes, roadsides, especially in sandy places. Anhui, Fujian, Jiangsu, Jiangxi, Taiwan, Xizang, Zhejiang [Afghanistan, Bhutan, Kyrgyzstan, Pakistan, S Russia, Tajikistan, Turkestan, Uzbekistan; Africa (N and on mountains), SW Asia, Europe].
This species is adventive in most temperate parts of the world. Vulpia alpina L. Liu (Fl. Reipubl. Popularis Sin. 9(2): 405. 2002), based on a single specimen from Xizang (Lhasa), may be simply a depauperate form of this species. The type has not been seen.