4. Poa compressa L. (Canada bluegrass)
Pl. 181 g,
h; Map 728
Plants perennial, with well‑developed rhizomes,
forming clumps or loose colonies. Flowering stems 20–70 cm long, erect but
often with prostrate bases, strongly flattened and 2‑edged, at least in
the apical 1/2, glabrous. Leaf sheaths keeled, glabrous or slightly roughened,
the ligule 0.7–2.0 mm long, truncate on the margin. Leaf blades 2–15 cm long,
1.5–4.0 mm wide, flat or more commonly folded toward the base, glabrous or
roughened along the margins. Inflorescences 2–10 cm long, usually narrow and
relatively dense, the lowermost nodes with 2(–4) branches, these strongly
ascending at maturity. Spikelets 3–8 mm long, with 3–6(–9) fertile florets.
Lower glume 1.5–3.0 mm long, lanceolate, sharply pointed at the tip, with
broad, thin margins, 1‑ or 3‑nerved, roughened along the midnerve.
Upper glume 1.8–3.5 mm long, elliptic‑ovate, sharply pointed at the tip,
with broad, thin margins, 3‑nerved, roughened along the midnerve. Lemmas
2–3 mm long, elliptic, sharply pointed at the tip, 3‑ or 5‑nerved,
short‑hairy along the keel and the outermost pair of lateral nerves, and
sometimes with a tuft of long, cobwebby hairs at the base. Anthers 1.0–1.7 mm
long. Fruits 1.2–1.5 mm long, yellow to yellowish brown. 2n=14, 35, 39,
42, 45, 49, 50, 56. May–August.
Introduced, scattered nearly throughout the state (native of
Europe, naturalized widely in the U.S. and Canada). Openings of mesic to dry
upland forests (particularly grazed sites), upland prairies, and glades; also
pastures, fallow fields, roadsides, railroads, and open, disturbed areas.
This species sometimes is cultivated as a lawn grass, mostly
on athletic fields and other high‑use areas. It also has been cultivated
as a pasture grass for forage in areas of poor soil where P. pratensis
does not grow well. Steyermark (1963) noted that the pollen is an important
causal agent of hay fever during the summer months.