GrassBase - The Online World Grass Flora


W.D. Clayton, M. Vorontsova, K.T. Harman & H. Williamson

© Copyright The Board of Trustees, Royal Botanic Gardens, Kew.

Poa occidentalis

HABIT Perennial; caespitose; clumped loosely. Butt sheaths herbaceous; red. Culms geniculately ascending, or decumbent; robust; 20–110 cm long. Culm-internodes terete; scaberulous. Leaves cauline. Leaf-sheaths with 0.25–0.5 of their length closed; longer than adjacent culm internode; keeled; retrorsely scabrous. Ligule an eciliate membrane; 3–12 mm long; scaberulous on abaxial surface; obtuse. Leaf-blades 4–18 cm long; 1.2–5.5(–10) mm wide; glaucous. Leaf-blade surface scabrous; glabrous. Leaf-blade apex hooded.

INFLORESCENCE Inflorescence a panicle.

Panicle open; pyramidal; 12–40 cm long; with spikelets clustered towards branch tips. Primary panicle branches spreading, or reflexed; 3–5 -nate; 5–23 cm long. Panicle branches scabrous.

Spikelets solitary. Fertile spikelets pedicelled.

FERTILE SPIKELETS Spikelets comprising 2–7 fertile florets; with diminished florets at the apex. Spikelets oblong; laterally compressed; 3–8 mm long; breaking up at maturity; disarticulating below each fertile floret. Rhachilla internodes obscured by lemmas; smooth. Floret callus woolly.

GLUMES Glumes persistent; similar; shorter than spikelet. Lower glume oblong; 0.9 length of upper glume; membranous; 1-keeled; 1 -veined. Lower glume lateral veins absent. Lower glume apex acute. Upper glume lanceolate; 0.9 length of adjacent fertile lemma; membranous; 1-keeled; 1–3 -veined. Upper glume lateral veins absent, or obscure. Upper glume apex acute.

FLORETS Fertile lemma oblong; elliptic in profile; 2.6–4.2 mm long; membranous; much thinner above; much thinner on margins; mid-green, or purple; keeled; 5 -veined. Lemma midvein ciliate; hairy below. Lemma surface puberulous; hairy on veins. Lemma margins ciliate; hairy below. Lemma apex obtuse. Palea 0.9 length of lemma. Palea keels scaberulous; adorned above. Apical sterile florets resembling fertile though underdeveloped.

FLOWER Lodicules 2; membranous. Anthers 3; 0.3–1 mm long; eventually exserted, or retained within floret.

FRUIT Caryopsis with adherent pericarp. Hilum punctiform.

DISTRIBUTION North America: western Canada, northwest USA, south-central USA, and Mexico.

NOTES Poeae. Soreng 1992.

Please cite this publication as detailed in How to Cite Version: 3rd February 2016.