Poa annua L.

annual bluegrass


Info

Subfamily: Pooideae
Genus etymology: Poa is the ancient Greek name for a herb of grass
Species etymology: annua = "lasting a year" [Latin] referering to its annual habit
Photosynthetic type: C3 (cool season)
Nativity: naturalized - accidental
First recorded in Hawaiʻi: 1838

Map

 Distribution of Poa annua in Hawaiʻi.
 Distribution of Poa annua in Hawaiʻi.

Inflorescence

Poa annua Inflorescence
Poa annua Inflorescence
Poa annua Inflorescence
Poa annua Inflorescence
Poa annua Inflorescence
Poa annua Inflorescence

Plant

Poa annua Plant
Poa annua Plant

Habit

Poa annua Habit

Spikelets

Poa annua Spikelets
Poa annua Spikelets
Poa annua Spikelets
Poa annua Spikelets

Collar

Poa annua Collar

Description

Loosely to compactly tufted annual or short-lived perennial; culms 2.5–30 cm. high, erect, spreading or prostrate. Leaf-blades 1–14 cm. long and 1–5 mm. wide, weak, often crinkled when young, blunt at the tip; ligule 2–5 mm. long. Panicle ovate or triangular, 1–12 cm. long, open and loose or somewhat dense. Spikelets 3–10-flowered, ovate or oblong, 3–10 mm. long; lower glume lanceolate to ovate, 1.5–3 mm. long, 1-nerved; upper glume elliptic or oblong, 2–4 mm. long, 3-nerved, broadest at about the middle; lemmas broadly elliptic with prominent white hyaline margins, 2.5–4 mm. long, obtuse to emarginate (obtuse in side view), glabrous or hairy on the nerves; palea-keels glabrous or ciliate; anthers 0.7–1.2(–1.6) mm. long.
(Description source: Clayton, W.D. 1970. Flora of Tropical East Africa. Gramineae (Part 1). Crown Agents for Oversea Governments and Administrations, London. 176 pp. )

A caespitose delicate annual (very rarely perennial). Culms 2·5-30 cm. tall, 2-4-noded, erect, spreading or decumbent, sometimes rooting at the lower nodes, rather slender, terete, glabrous, smooth. Leaf-sheaths usually loose, somewhat compressed, keeled, smooth, usually glabrous. Ligule 2-5 mm. long. Leaf-laminae 1·5-10(15) x 0·1-0·5 cm., linear or linear-oblong, with the apex abruptly acute or often cucullate, expanded or folded, flaccid, scaberulous along the margins otherwise smooth, glabrous. Panicle 2-8(12) cm. long, open or more rarely contracted, ovate in outline, somewhat stiff; branches usually 2 (rarely 3-5)-nate or solitary, spreading at first, later usually slightly deflexed, smooth; pedicels 0·3-5 mm. long, smooth. Spikelets 3-8(10) mm. long, 3-7(10)-flowered, ovate to oblong in outline, usually crowded, green or often tinged with purple. Inferior glume 1·5-3 mm. long, 1-nerved, ovate or lanceolate; the superior 2-4·25 mm. long, 3-nerved, elliptic or oblong. Lemmas 2·3-4·25 mm. long, broadly elliptic or ovate-elliptic with white hyaline margins, with the apex obtuse. Anthers 0·7-1·2(1·6) mm. long. Caryopsis 1-2 mm. long.
(Description source: Launert, E. & Pope, G.V. (eds.). 1989. Flora Zambesiaca. Volume 10. Part 3. Kew, London. 152 pp )

Plants usually annual, rarely surviving for a second season; not rhizomatous, sometimes stoloniferous, densely tufted. Basal branching intravaginal, innovations common, similar to the culms. Culms 2-20(45) cm, prostrate to erect, slender; nodes terete, usually 1 exserted. Sheaths closed for about 1/3 their length, terete or weakly compressed, smooth; ligules 0.5-3(5) mm, smooth, glabrous, decurrent, obtuse to truncate; blades 1-10 cm long, 1-3(6) mm wide, flat or weakly folded, thin, soft, smooth, margins usually slightly scabrous, apices broadly prow-shaped. Panicles 1-7(10) cm, lengths 1.2-1.6 times widths, erect; nodes with 1-2(3) branches; branches ascending to spreading or reflexed, straight, terete, smooth, with crowded or loosely arranged spikelets. Spikelets 3-5 mm, laterally compressed; florets 2-6; rachilla internodes smooth, glabrous, concealed or exposed, distal internodes less than 1/2(3/4) the length of the distal lemma. Glumes smooth, distinctly keeled, keels smooth; lower glumes 1-veined; upper glumes shorter than or subequal to the lowest lemma; calluses glabrous; lemmas 2.5-4 mm, lanceolate, distinctly keeled, smooth throughout, the keels, marginal veins, and, usually, lateral veins crisply puberulent to long-villous, rarely glabrous throughout, lateral veins prominent, intercostal regions glabrous, margins smooth, glabrous, apices obtuse to acute; palea keels smooth, usually short- to long-villous, rarely glabrous; anthers 0.6-1.1 mm, oblong prior to dehiscence, those of the upper 1-2 florets usually vestigial. 2n = 28.
(Description source: Barkworth, M.E., Capels, K.M. & Long, S. (eds.) 1993. Flora of North America, north of Mexico. Volume 24. Magnoliophyta: Commelinidae (in part): Poaceae, Part 1. Oxford University Press, New York. 911 pp. http://floranorthamerica.org/Poa_annua )

Bright green annuals; culms spreading or sometimes erect, rooting at nodes and forming mats, 0.3-2(-3.5) dm tall, strongly flattened. Sheaths open ca. 1/2 their length, with overlapping margins; ligule 1-3 mm long, obtuse or truncate, often erose; blades lax, folded or flat, 1-10 cm long, 1- 2.5(-3) mm wide, margins scaberulous, otherwise glabrous. Panicles open, pyramidal, 1.5-3.5(-8) cm long, branches spreading, usually rigid; spikelets 3-6-flowered, (3-)4-5.5(-7) mm long, rachilla elongate; glumes glabrous, first glume narrowly lanceolate, 1.5-2.2 mm long, 1-nerved, apex acute, second glume oblanceolate to obovate, slightly longer than first glume, 1.8- 2.7 mm long, 1-3-nerved, somewhat obtuse; lemmas 2.5-3.5 mm long, prominently 5-nerved, the nerves villous toward base, the margins scarious toward apex, pilose toward base; palea 1.5-2 mm long, 2- nerved, keeled, nerves villous, margins hyaline. Caryopsis pale brown, ellipsoid, somewhat trigonal, ca. 1 mm long. [22 = 14, 24-26, 28, 52.]
(Description source: O’Connor, P.J. 1990. Poaceae, pp. 1481–1604. In: Wagner W.L., Herbst D.R. & Sohmer S.H. (eds.)., Manual of the flowering plant of Hawaiʻi. Vol. 2. University of Hawaii Press & Bishop Museum Press, Honolulu )