Description from Flora of China
Perennials, densely tufted; shoots all or mostly extravaginal, all or most shoots flowering. Culms erect to ascending, 20–60 cm tall, 0.5–1.5 mm in diam., rounded, smooth, not or only slightly ridged, nodes 2 or 3, 1 or 2 exserted. Leaf sheaths moderately firm, not persisting, not shiny, 4–10 cm, 1/2–2/3 as long as blade, lower sheaths glabrous or scabrid to retrorsely strigose near collars, uppermost closed for 1/4–1/2 of length; blade flat or folded with margins slightly inrolled, thin, 5–10 cm × 1–2 mm, surfaces smooth or scabrid, adaxially glabrous or retrorsely strigulose near base, margins scabrid; ligule 0.5–2 mm, apex dentate, collar margins glabrous or with some cilia. Panicle open, 6–13 × 2–7 cm, longest internodes 1.4–3.5 cm; branches flexuous, 2 or 3 per node, slender, proximally rounded and smooth, distally scabrid and weakly angled, longest 2–8 cm with 3–10 spikelets in distal 1/2. Spikelets green or purple tinged, 4–7 mm, florets 2–4; vivipary absent; rachilla internodes to 1.2 mm, smooth or scabrid; glumes unequal, lanceolate, usually purple, apex acuminate, lower glume 2–2.5 mm, 1-veined, upper glume 2.7–3.5 mm, keel scabrid to coarsely ciliate near apex, smooth elsewhere, distinctly shorter than first lemma; lemmas 3.3–4.8 mm, apex sharply acute to acuminate, intermediate veins faint to moderately distinct, keel lower part and marginal veins scabrid, glabrous or for 1/3 of length sparsely pilulose, area between veins scabrid to minutely bumpy throughout; callus glabrous, or infrequently with a few hairs to 2 mm; palea smooth or scabrid, glabrous between keels, keels scabrid. Anthers 1.5–2.3 mm. Fl. and fr. Jun–Aug.
Poa perennis in its typical form is distinct from all other Poa species. The circumscription is challenging because many specimens do not agree in detail with the type, but are not readily assignable to other species. We have not seen any material from Xizang, but it is expected to occur there.
* Grassy places on gravel slopes; 2500–3500 m. ?SE Xizang, NW Yunnan.