1	Cells on nutlet surface transversely oblong with an elevated margin resulting in nutlet surface transversely undulately striate or scabrously rugose		(2)
+	Cells on nutlet surface hexagonally reticulately striate or puncticulate		(4)
2 (1)	Culms 10-35 cm tall; spikelets narrowly oblong-ovoid to narrowly linear-ovoid, 0.8-2 cm × 3-3.5 mm, 16-30-flowered; glumes brown to dark brown.		9 P. diaphanus
+	Culms 3-15 cm tall; spikelets ovoid, oblong-ovoid, or narrowly ovoid, 5-15 cm × 2.5-4 mm, 8-16-flowered; glumes straw-colored, yellowish brown, or purplish red		(3)
3 (2)	Culms slender; leaves 0.3-1.5 mm wide; anthela rays very short; spikelets 1 to several per ray, nearly fascicled; glumes purplish red to reddish brown on both surfaces.		10 P. setiformis
+	Culms slightly thick; leaves 1-3 mm wide; anthela rays mostly to 2.5 cm; spikelets 3-8 per ray, congested; glumes straw-colored to yellowish brown.		11 P. pseudolatespicatus
4 (1)	Glumes broadly sulcate on both surfaces.		8 P. sanguinolentus
+	Glumes not broadly sulcate on both surfaces		(5)
5 (4)	Glume apices truncate to emarginate and excurved mucronate to awned.		7 P. pumilus
+	Glume apices obtuse or acute and not excurved mucronate		(6)
6 (5)	Spikelets narrowly linear-ovate, narrowly ovoid, narrowly oblong-ovoid, or oblong-ovoid; glumes densely imbricate, ca. 3 mm or more; stamens 3		(7)
+	Spikelets linear, linear-oblong, narrowly linear-ovoid, or narrowly ovoid; glumes slightly laxly imbricate or rarely densely imbricate, 1.5-2 mm; stamens 1 or 2		(8)
7 (6)	Spikelets ca. 2.5(-3) mm wide; glumes blackish brown.		1 P. delavayi
+	Spikelets 3-5 mm wide; glumes straw-colored or yellowish brown.		2 P. unioloides
8 (6)	Nutlet oblong, both surfaces concave sulcate; stamen 1.		6 P. sulcinux
+	Nutlet obovoid-oblong or obovoid, both surfaces not concave sulcate; stamens (1 or)2		(9)
9 (8)	Anthelae with very short rays; spikelets narrowly ovoid to narrowly linear-ovoid; glumes subelliptic, abaxially not conspicuously keeled.		5 P. lijiangensis
+	Anthelae simple, lax, usually with slightly long or rarely very short rays; spikelets linear-oblong or linear; glumes oblong-ovate or subovate, abaxially keeled		(10)
10 (9)	Spikelets radiately arranged; rachilla 4-angled, with trabeculae in both lateral sulculi; glumes brown to dark brown, laxly imbricate, apex obtuse; anthers oblong.		3 P. flavidus
+	Spikelets suberect; rachilla flexuose, narrowly winged; glumes straw-colored to rarely pale brown, densely imbricate, apex sometimes mucronate; anthers linear.		4 P. polystachyos