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Descriptions

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

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

Poa arida

HABIT Perennial; caespitose. Rhizomes elongated. Butt sheaths herbaceous. Culms 15–80 cm long. Culm-internodes terete; striate; smooth, or scaberulous. Lateral branches lacking. Leaves mostly basal. Leaf-sheaths with 0.2 of their length closed; glabrous on surface. Ligule an eciliate membrane; 1–4 mm long; entire, or lacerate; acute. Leaf-blades flat, or conduplicate; 3–12 cm long; 1–5 mm wide; 1–6 cm long at summit of culm; light green, or glaucous. Leaf-blade surface glabrous.

INFLORESCENCE Inflorescence a panicle.

Panicle open; lanceolate; 4–12 cm long. Primary panicle branches appressed; 2–3 -nate. Panicle branches scabrous.

Spikelets solitary. Fertile spikelets pedicelled.

FERTILE SPIKELETS Spikelets comprising 3–7 fertile florets; with diminished florets at the apex. Spikelets ovate; laterally compressed; 4–7 mm long; breaking up at maturity; disarticulating below each fertile floret. Rhachilla internodes smooth; pubescent. Floret callus glabrous.

GLUMES Glumes persistent; similar; shorter than spikelet. Lower glume oblong; 2.5–3.5 mm long; 0.9 length of upper glume; membranous; 1-keeled. Lower glume primary vein smooth, or scaberulous. Lower glume apex acute. Upper glume oblong; 2.5–4 mm long; 0.66–0.75 length of adjacent fertile lemma; membranous; 1-keeled; 3 -veined. Upper glume primary vein smooth, or scaberulous. Upper glume apex acute.

FLORETS Fertile lemma oblong; elliptic in profile; 2.5–4 mm long; membranous; keeled; lightly keeled; 5 -veined. Lemma midvein ciliolate; hairy below. Lemma lateral veins prominent. Lemma surface scabrous; pilose; hairy below; hairy on veins. Lemma margins ciliolate; hairy below. Lemma apex obtuse, or acute. Palea 0.9 length of lemma. Palea keels ciliolate, or ciliate; adorned above. Apical sterile florets resembling fertile though underdeveloped.

FLOWER Lodicules 2; membranous. Anthers 3; 1.3–1.7 mm long.

FRUIT Caryopsis with adherent pericarp. Hilum punctiform.

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

NOTES Poeae. Soreng 1992.

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