Poa annua var. reptans

Annuals, sometimes over wintering, infrequently stoloniferous. Culms loosely tufted, erect or oblique, often decumbent, often geniculate, soft, 6–30(–45) cm tall, smooth, nodes 1 or 2(or 3), 1(or 2) exserted. Leaf sheath slightly compressed, thin, smooth, uppermost closed for ca. 1/3 of length; blade light to dark green, flat or folded, thin, 2–12 cm × (0.8–)1–3.5 mm, margins slightly scabrid, apex acutely prow-tipped; ligules 0.6–3 mm, abaxially smooth, glabrous, apex obtuse, margin irregularly dentate, smooth. Panicle open, moderately congested, broadly ovoid to pyramidal, (1–)3–10 cm, as long as wide; branches ascending, spreading, or a few reflexed, 1 or 2(–3) per node, smooth, longest with usually 3–5 spikelets in distal 1/2. Spikelets ovate to oblong, dark to light green, (3–)4–5.5 mm, florets 3–5, distal fertile florets often female; vivipary absent; rachilla internodes 0.5–1.5 mm, smooth, glabrous, hidden or exposed; glumes unequal, smooth or rarely keeled with hooks, lower glume lanceolate and acute to subflabellate and obtuse, 1.5–2(–3) mm, 1-veined, upper glume elliptic, 2–3(–4) mm, 3-veined, the margin angled; lemmas ovate, 2.2–3.5 mm, apex and margins broadly membranous, intermediate veins prominent, keel and marginal, and usually intermediate, veins villous in the lower 1/2, rarely glabrous throughout; callus glabrous; palea keels smooth, densely pilulose to short villous. Anthers 0.6–1 mm, usually at least 2 × as long as wide, or vestigial. Fl. Apr–May, fr. Apr–Jul. 2n = 28.

This dwarf grass is easy to overlook, particularly when it grows in close proximity to other grasses. For a Poa sp. (bluegrass), it has short leaf blades and rather plump-looking seedheads. It is fairly easy to identify because of its small size and low sprawling stems. To determine the technical characteristics of this and other bluegrasses, it is highly desirable to use a good 10x hand lens, or even a field microscope. Such instruments can be used to detect the presence (or absence) of hairs along the veins and bases of the lemmas. Some bluegrasses superficially resemble Eragrostis spp. (love grasses), but the latter have tufts of hair at the junctions of their blades and sheaths. Bluegrasses lack such tufts of hair.

Poa annua is easily distinguished from other short-anthered Poa, other than P. infirma, by the annual habit, absence of a web on the callus, and the near absence of hooks on the panicle branches and spikelet bracts, in combination with densely pubescent palea keels that lack hooked prickle hairs at the apex. Plants with glabrous florets are sporadically encountered.

Plants perennating by short stolons rooting at the nodes appear to develop repeatedly but sporadically at various elevations with prolonged, cool, mesic growing conditions, possibly in response to trampling. These are sometimes placed in var. reptans. Such plants have been recorded from Yunnan.

"Annuals; culms 15-20 cm high, tufted; nodes glabrous. Leaves 5-10 x 0.2-0.3 cm; rounded at base, glabrous; sheath keeled, glabrous; ligule membranous. Panicle 5-6 x 2 cm, contracted; branches filiform, glabrous. Spikelets similar, 5-6 mm long, ovate, glabrous; lower glume 2 x 0.5 mm, lanceolate, 1-nerved; upper glume 2.5 x 1 mm, ovate, acute, 3-nerved; florets 2-4, similar; upper florets exerted; lemmas 3 x 1 mm, ovate-lanceolate, 3-5-nerved, hairy along the nerves; palea 3 x 0.75 mm, lanceolate, 2-nerved; stamens 3; ovary oblong; style short or absent."