4. Poa subg. Poa
早熟禾亚属 zao shu he ya shu
Authors: Guanghua Zhu, Liang Liu & Robert J. Soreng
Annuals or perennials, with or without rhizomes, without bulbs; shoots extravaginal and intravaginal. Sheaths sometimes strongly keeled, uppermost closed for more than (1/5–)1/4 of length; ligules membranous, milky-white or hyaline. Panicle with or without unisexual flowers, loosely contracted to open; branches smooth or scabrid, round or angled; lower glumes 1- or 3-veined; lemmas distinctly keeled, glabrous or pubescent, outer margin smooth or sparsely scabrid, glabrous, intermediate veins faint or more commonly conspicuous; callus glabrous or mostly dorsally webbed, rarely diffusely villous; palea keels glabrous or pubescent, usually scabrid at least distally. Anthers 0.2–4 mm.
About 400 species:distribution as for genus; 51 species (13 endemic) in China.
The Chinese species belong to three sections: Poa sect. Macropoa F. Hermann ex Tzvelev (species nos. 13–16); P. sect. Poa (species nos. 17–29), which is further subdivided into P. subsect. Nivicolae (Roshevitz) Tzvelev (species nos. 17–19), P. subsect. Poa (species nos. 20–22), and P. subsect. Cenisiae (Ascherson & Graebner) V. Jirásek (species nos. 23–29); and P. sect. Homalopoa Dumortier (species nos. 30–63).
Poa raduliformis (species no. 22) could not be included in Key 2 below because the taxon is insufficiently known to the authors. No specimens definitely referable to P. raduliformis were seen for this treatment.