3. Poa chapmaniana Scribn. (Chapman bluegrass)

Pl. 181 f; Map 727

Plants annual, without rhizomes, forming tufts. Flowering stems 6–25 cm long, spreading to more commonly erect or ascending, circular in cross‑section or slightly flattened, glabrous. Leaf sheaths rounded, glabrous, the ligule 0.5–2.6 mm long, rounded to truncate on the margin. Leaf blades 1–8 cm long, 0.5–2.5 mm wide, flat or sometimes with the margins loosely inrolled, glabrous. Inflorescences 2–7 cm long, open, the lowermost branches single or paired, ascending to spreading or less commonly loosely reflexed. Spikelets 2.3–4.5 mm long, with 2–6 fertile florets. Lower glume 1.5–2.2 mm long, lanceolate, sharply pointed at the tip, with broad, thin margins, 1‑nerved, roughened along the midnerve. Upper glume 1.7–2.6 mm long, narrowly ovate, sharply pointed at the tip, with broad, thin margins, 3‑nerved, roughened along the midnerve. Lemmas 1.6–2.6 mm long, elliptic, bluntly pointed at the tip, 3‑nerved (an additional, very faint pair of lateral nerves sometimes present), short‑hairy along the nerves and with a tuft of long, cobwebby hairs at the base. Anthers 0.1–0.3 mm long, included in the spikelet at maturity. Fruits 1.0–1.2 mm long, brownish yellow. April–May.

Scattered nearly throughout the state, but absent or uncommon in some parts of northern Missouri (southeastern U.S. north to Delaware and Nebraska, occasionally introduced farther north). Margins and openings of bottomland and more commonly mesic to dry upland forests, glades, upland prairies, pastures, margins of crop fields, fallow fields, roadsides, railroads, and disturbed, open areas, often on acidic substrates.

Poa chapmaniana is very closely related to P. annua. Some authors combine the two and treat it as a native phase of that species. The two differ primarily in that P. chapmaniana has lemmas with cobwebby bases and smaller anthers. The stamens and stigmas usually remain included in the spikelets during flowering, with the lemmas remaining appressed at maturity, and the plants thus are nearly obligately self‑pollinated (cleistogamous). In Missouri, this species is less frequently encountered than P. annua, but it is probably overlooked by some collectors who mistake plants of P. chapmaniana for that species.