1	Leaf blades flat; tillers extravaginal, with cataphyllous shoots present; spikelets (1.8–)1.9–2.5 mm long; from Argentina and Chile (P.sesquiflora) or Mexico (P.liebmannii, P.rosei)	2
–	Leaf blades involute or convolute, filiform or acicular; tillers intravaginal, cataphyllous shoots absent; spikelets 1–2 mm long, or 2.8–4.2 mm long in P.colombiana; from NW South America (P.colombiana, P.trichodes), Guatemala (P.exserta), or Costa Rica and Panama (P.bacillata)	4
2	Panicle contracted and slender, 2–6.5 × 0.25–1 cm, spikelets present from near the base; callus with short hairs 0.1–0.2 mm long; rachilla extension distinct, 0.2–0.4 mm long, often with short hairs distally; from Argentina and Chile	P.sesquiflora (E. Desv.) Parodi ex Nicora
–	Panicle usually lax and open, less often contracted, 7–18 × (1–)2.5–7 cm, spikelets in the distal 1/3, the lower 2/3 naked; callus glabrous; rachilla extension distinct, 0.3–0.5 mm long, or rudimentary and sometimes absent, glabrous; from Mexico	3
3	Lemmas with a well-developed awn inserted in the lower 1/3, straight or geniculate, reaching the apex of the lemma or glumes or briefly surpassing them; leaf blades usually dimorphic, those of the tillers filiform and narrow, 0.2–0.6(–1) mm wide when opened out, flat or folded, those of the culm 1–2.6 mm wide, flat or slightly convolute towards their apices	P.rosei (Scribn. & Merr.) Sylvester & Soreng
–	Lemmas awnless; leaf blades not notably different between tillers and culm, filiform or flat, (0.5–)1–3.5 mm wide	P.liebmannii (E. Fourn.) Sylvester & Soreng
4	Panicle contracted and slender, < 1.2 cm wide, spikelets present from near the base; spikelets 2.8–4.2 mm long; upper glume 3-veined; plants forming small tussocks with a basal mat of leaves 5–26 cm tall	P.colombiana Sylvester & Soreng
–	Panicle lax and open, 1–8 cm wide, spikelets in the distal 1/3, the lower 2/3 naked; spikelets 1–2 mm long; upper glume usually 1-veined, sometimes 3-veined in P.trichodes; plants forming short tufts with a basal mat of leaves often < 10 cm tall (to c. 17 cm tall in P.bacillata)	5
5	Leaf blade abaxial surface finely to densely scabrous; culms usually with at least one elongated internode visible (not including the terminal culm segment below the panicle), with at least 1 node usually visible at flowering; basal mat of leaves usually 6–13 cm tall, to 17 cm tall; leaf blades 2–15 cm long; ligules 1.7–4.3 mm long; panicles 4–11 cm long, panicle branches and pedicels smooth; spikelets 1.7–2 mm long; glume keels scaberulous just in the distal 1/3, surfaces smooth; lemmas smooth; rachilla 0.3–1.4 mm long; from páramos of Costa Rica and Panama	P.bacillata (Hack.) Sylvester & Soreng
–	Leaf blade abaxial surface finely to densely scabrous (P.trichodes) or smooth (P.exserta); culms usually without visible elongated internodes (NB. this does not refer to the terminal culm segment below the panicle), with 0(–1) nodes visible at flowering; basal mat of leaves usually < 5 cm tall, to 10 cm tall; leaf blades 1–4 cm long, rarely longer, lightly to densely scabrous or smooth; ligules 1–2(–2.5) mm long; panicles 2–5(–6) cm long, panicle branches and pedicels smooth (P.exserta) or usually lightly to densely scabrous (P.trichodes); spikelets 1–2 mm long; glume keels scabrous just in the distal 1/3 to throughout their length, surfaces smooth or scabrous distally; lemmas smooth (P.exserta) or lightly to densely scabrous (P.trichodes); rachilla 0.2–0.5 mm long; from various localities, not found in Costa Rica or Panama	6
6	Leaf blade abaxial surface moderately to usually densely scabrous; spikelets 1–1.5 mm long; glume keels scabrous just in the distal 1/3 to throughout their length, surfaces smooth or scabrous distally; lemmas moderately to densely scabrous; panicle branches usually lightly scabrous, infrequently smooth; pedicels usually lightly scabrous, rarely smooth; from Colombia and Venezuela to Peru	P.trichodes (Kunth) Sylvester & Soreng
–	Leaf blade abaxial surface smooth; spikelets (1.2–)1.5–2 mm long; glume keels scaberulous just in the distal 1/3, surfaces smooth; lemmas smooth; panicle branches smooth; pedicels smooth; from Guatemala	P.exserta (Swallen) Sylvester & Soreng