9. Poa trivialis L. (rough bluegrass)

Pl. 180 c, d; Map 733

Plants perennial, without rhizomes but sometimes appearing stoloniferous because of the prostrate stem bases that root at the lowermost nodes, forming loose clumps or tufts. Flowering stems 40–100 cm long, erect but often prostrate at the base, circular in cross‑section or very slightly flattened, glabrous or roughened toward the tip. Leaf sheaths rounded or nearly so, roughened with minute, downwardly pointing hairs, the ligule 2–8 mm long, rounded or bluntly pointed on the margin. Leaf blades 5–20 cm long, 2–6 mm wide, flat, glabrous or roughened on the upper surface. Inflorescences 6–20 cm long, open or narrow and appearing dense, the lowermost nodes with 5–8 branches, these ascending at maturity. Spikelets 2.5–4.5 mm long, with 2 or 3 fertile florets. Lower glume 1.7–2.9 mm long, lanceolate, sharply pointed at the tip, 1‑nerved, roughened along the midnerve. Upper glume 2.0–3.3 mm long, oblong‑lanceolate, sharply pointed at the tip, with broad, thin margins, 1‑ or 3‑nerved, roughened along the midnerve. Lemmas 2.5–4.0 mm long, narrowly elliptic‑ovate, sharply pointed at the tip, 5‑nerved, glabrous except for the tuft of cobwebby hairs at the base and the minutely hairy, roughened midnerve. Anthers 1–2 mm long. Fruits 1.2–1.5 mm long, yellow, shiny. 2n=14, 15, 28, 42. May–June.

Introduced, uncommon and widely scattered in Missouri (native of Europe, introduced widely in the northern U.S. and adjacent Canada south to North Carolina and California). Margins of springs and lakes; also railroads and moist, disturbed areas.

Poa trivialis sometimes is included in grass seed mixes for shaded sites. Steyermark (1963) noted that in some portions of its range, pollen of this species is an important causal agent of hay fever.