244 MISC. PUBLICATION 243, U.S. DEPT. OF AGRICULTURE 
Culms delicate, usually less than 40 em tall, spikelets not- 
more than 1.5 mm long (Enszfolia). 
Spikelets about 1 mm long; blades not white-margined. 
82. P. CHAMAELONCHE. 
Spikelets about 1.5 mm long; blades white-margined. 
Uppermost culm blades much reduced. 
80. P. ALBOMARGINATUM. 
Uppermost culm blades about as long as the others. 
81. P. TRIFOLIUM. 
2b. Basal leaves similar to the culm leaves, not forming a winter rosette; 
spikelets all fertile. 
oa. Plants annual. 
Spikelets laterally compressed; second glume carinate. Panicles small, 
fEy~HOWELEO. 52 see 2 Sic ee REI AR ee rs ae eee 53. P. TRIGONUM. 
Spikelets not laterally compressed; second glume not carinate. 
Spikelets plano-gibbous, the second glume swollen, bristly and burlike 
at maturity; first glume nearly as long as the minute spikelet. 
58. P. HIRTUM. 
Spikelets not plano-gibbous nor burlike. 
Panicles consisting of more or less secund spikelike racemes; fruit. 
transversely rugose; glumes and sterile lemma usually reticulate- 
veined (Fasciculata). 
Spikelets strongly reticulate-veined, 2 to 3 mm long, glabrous. 
4, P. FASCICULATUM. 
Spikelets scarcely reticulate-veined or only near the apex. 
Spikelets not more than 2 mm long, glabrous__ 38. P. REPTANS. 
Spikelets more than 3 mm long, pubescent. 
Rachis pilose with bristly hairs; plants more or less velvety. 
P. MOLLE. 
Rachis scabrous but not bristly. 
Spikeletselabrouses sop esi ae eee 7. .P. ADSPERSUM. 
Spikelets tuberculate-hispid________- 6. P. ECHINULATUM. 
Panicles more or less diffuse. 
Bladesiovate=lanceola te, 22s = ee 43. P. TRICHOIDES. 
Blades linear. 
First glume not more than one-fourth the length of the spikelet,. 
truncate or triangular-tipped____ 8. P. DICHOTOMIFLORUM. 
First glume usually as much as half the length of the spikelet,. 
acute or acuminate. 
Inflorescence elongate, composed of several approximate impli- 
Cate; panicless ae) 2 heap ek ee 15. P. CcAYENNENSE. 
Inflorescence not as above. 
Panicles more than half the length of the entire plant. 
. P. CAPILLARE. 
Panicles not more than one-third the entire height of the 
PLAT G soe eee ee 14. P. HIRTICAULE. 
ob. Plants perennial. 
6a. Spikelets short-pediceled along one side of the panicle branches, form- 
ing more or less spikelike racemes. 
Spikelets more or less pubescent or hispid. 
Spikelets 4 mm long; blades 2 to 4cm wide__ 55. P. ASPERIFOLIUM. 
Spikelets less than 3 mm long; blades mostly less than 1 ecm wide. 
Sterile lemma glandless; second glume inflated-gibbous. 
48. P. VENEZUELAE. 
Sterile lemma bearing a pair of crateriform glands. 
41, P. PULCHELLUM. 
Spikelets glabrous. 
Blades lanceolate or ovate-lanceolate; glumes strongly carinate. 
Blades not more than 5 em, usually 2 or 3 cm, long; second glume 
rather blunt and shorter than the sterile lemma. 
39. P. STOLONIFERUM. 
Blades 5 to 11 em long; second glume acute, nearly equaling the 
SUCEIG lemumay |. 5 Leia See ee 40. P. FRONDESCENS. 
