9. Poa infirma Kunth in Humboldt et al. in Humboldt et al., Nov. Gen. Sp. 1: 158. 1816 [“1815”].
低矮早熟禾 di ai zao shu he
Poa annua Linnaeus subsp. exilis (Tommasini ex Freyn) Ascherson & Graebner; P. annua var. exilis Tommasini ex Freyn; P. exilis (Tommasini ex Freyn) Murbeck.
Annuals. Culms loosely tufted, erect or oblique, often decumbent, often geniculate, soft, 5–25 cm tall, smooth, nodes 1 or 2(–3), 1(or 2) exserted. Leaf sheaths, thin, smooth, uppermost closed for ca. 1/3 of length; blade light green, flat or folded, thin, 2–8 cm × 1–3 mm, margins smooth or sparsely scabrid, apex acutely prow-tipped; ligule membranous, 1–3 mm, abaxially smooth, glabrous. Panicle open, ovoid-oblong, 2–10 cm, 1–2 × as long as wide; branches ascending, 1–3 per node, smooth, longest usually with 5–9 moderately crowded spikelets in distal 1/2. Spikelets ovate to oblong, light green, 3–4 mm, florets 4–6, distal fertile florets often female; vivipary absent; rachilla internodes 1–1.5 mm, smooth, glabrous, often exposed; glumes unequal, margins broadly membranous, smooth, lower glume lanceolate and acute to subflabellate and obtuse, 1–1.5 mm, 1-veined, upper glume elliptic, margin angled, 1.8–2.5 mm, 3-veined; lemmas ovate, membranous-papery, 2–2.5 mm, keel densely villous, marginal and lateral veins densely villous; callus glabrous; palea keels without hooks, densely pilulose to short-villous. Anthers 0.2–0.5 mm, round to short elliptical, less than 1.5 × as long as wide, or vestigial. Fl. and fr. May–Aug. 2n = 14.
Sporadic in moist meadows, gardens, sandy places, shady disturbed ground; 1000–2000 m. Fujian, Shanxi, Sichuan, Zhejiang [India, Pakistan, Tajikistan; Africa, SW Asia, Australia, Europe, Japan, New Zealand, North America, Pacific Islands, South America].
Poa infirma differs from P. annua in its shorter, more spherical or slightly lozenge-shaped anthers, and diploid chromosome number. It also has more ascending branches with more crowded spikelets.