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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 arachnifera

HABIT Perennial; caespitose. Rhizomes elongated. Butt sheaths herbaceous. Culms erect; 25–85 cm long. Culm-internodes terete. Leaf-sheaths with 0.33–0.5 of their length closed; keeled. Ligule an eciliate membrane; 1–4 mm long; acute. Leaf-blades flat, or conduplicate; 1.5–4.5 mm wide. Leaf-blade surface scaberulous; rough adaxially; glabrous.

INFLORESCENCE Dioecious. Inflorescence a panicle.

Panicle contracted; oblong; interrupted; 3–15 cm long. Primary panicle branches 2–4 -nate; 2–7 cm long; naked below, or bearing spikelets almost to the base. Panicle branches scabrous.

Spikelets solitary. Fertile spikelets pedicelled.

FERTILE SPIKELETS Spikelets comprising 2–5 fertile florets; with diminished florets at the apex. Spikelets oblong; laterally compressed; 4–9 mm long; breaking up at maturity; disarticulating below each fertile floret. Rhachilla internodes 0.5–0.9 mm long; smooth. Floret callus woolly.

GLUMES Glumes persistent; similar; shorter than spikelet. Lower glume lanceolate; 0.9 length of upper glume; membranous; 1-keeled; 1–3 -veined. Lower glume primary vein smooth, or scaberulous. Lower glume lateral veins absent, or obscure. Lower glume apex acute. Upper glume lanceolate; membranous; 1-keeled; 3–5 -veined. Upper glume primary vein smooth, or scaberulous. Upper glume apex acute.

FLORETS Fertile florets female. Fertile lemma oblong; elliptic in profile; 4.2–6.5 mm long; membranous; much thinner above; keeled; 5–7 -veined. Lemma midvein ciliate. Lemma surface smooth, or papillose; pubescent; hairy on veins. Lemma margins ciliate. Lemma apex acute. Palea 0.9 length of lemma. Palea keels ciliolate; adorned above. Apical sterile florets resembling fertile though underdeveloped.

FLOWER Lodicules 2; membranous. Anthers 3; 1.6–2.7 mm long.

FRUIT Caryopsis with adherent pericarp. Hilum punctiform.

MALE Male inflorescence similar to female. Male spikelets distinct from female; 2–10 flowered; 4–9 mm long; glabrous. Male spikelet lemma 3.5–5 mm long.

DISTRIBUTION Pacific: northwestern. North America: northwest USA, north-central USA, south-central USA, and southeast USA.

NOTES Poeae. Soreng 1992.

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