Part 3, 1915] 



P0AC3AE 



199 



Spikelets turgid, attenuate at base, mostly 

 pustulose-pubescent; leaf -blades conspicu- 

 ously striate, tapering from base to apex. 

 Spikelets scarcely turgid, not attenuate at base ; 

 leaf -blades tapering to both ends. 

 Leaf -blades not long and stiff (somewhat- so in P. 

 oligosanthes, P. malacon, P. Commonsianum, 

 and P. equilaterale) ; autumnal phase usually 

 not bushy-branched. 

 Plants not forming a distinct winter rosette; 



spikelets attenuate at base, papillose. 

 Plants forming a distinct winter rosette; 

 spikelets not attenuate at base. 

 Spikelets turgid, blunt, strongly nerved 

 (not strongly turgid in P. oligosanthes) ; 

 leaf -blades rarely as much as 1.5 cm. 

 wide (sometimes 2 cm. in P. Ravenelii 

 and P. xanthophysum). 

 Leaf-sheaths glabrous or minutely pu- 

 berulent; spikelets 1.5-2.5 mm. long, 

 asymmetrically pyriform; culms wiry. 

 Leaf -sheaths, or some of them, papillose- 

 hispid (sometimes all glabrous in P. 

 Heller i) ; spikelets Z—^ mm. long (2.7 

 -3 mm. in P. Wilcoxianum) . 

 Spikelets not • turgid, blunt, nor strongly 

 nerved (see, however, P. roanokense 

 and P. caerulescens) . 

 Ligule of conspicuous hairs, usually 3-5 

 mm. long. 

 Leaf-sheaths glabrous or only the 



lowermost somewhat pubescent. 

 Leaf-sheaths strongly pubescent. 

 Ligule obsolete or nearly so (manifest 

 in P. viscidellum, P. oricola, P. 

 tsugetorum and P. curiifolium) . 

 Spikelets spheric at maturity; 

 leaf -blades glabrous, firm, cordate; 

 plants sparingly branching. 

 Spikelets usually obovate or elliptic. 

 Leaf -blades of the mid-culm elon- 

 gate, less than 1.5 cm. wide; 

 culms usually tall; spikelets 

 pointed, abruptly so in the 

 velvety P. scoparium and P. 

 viscidellum. 

 Leaf -blades of the mid -culm not 

 elongate (somewhat so in 

 P. equilaterale). 

 Blades cordate, 1-3 cm. wide 

 (5-12 mm. in P. Ashei); 

 spikelets pubescent. 

 Spikelets 2.5-3 mm. long; 

 leaf-sheaths glabrous or 

 minutely puberulent. 

 Spikelets 3-5 mm. long 

 (sometimes but 2.7 mm. 

 long in the hispid- 

 sheathed P. eland estin- 

 um). 

 Blades not cordate (somewhat 

 in P. annulum), less than 

 1 cm. wide. 

 Sheaths crisp- or appressed- 

 pubescent; blades firm; 

 spikelets pubescent. 

 Sheaths glabrous (sparsely 

 pilose in P. curii- 

 folium and the lower 

 ones velvety in P. 

 mattamuskeetense and 

 often in P. annulum) . 

 Vernal culms delicate 

 (sometimes scarcely 

 so in P. albomargin- 

 atum and P. tenue) ; 

 spikelets 1.5 mm. 

 long or less (1.6-1.7 

 mm. in P. tenue). 



XXV. Angustifolia. 



XXVI. BlCKNELWANA. 



XXXIX. Pediceixata. 



XXXIV. Lancearia. 



XXXV. OUGOSANTHIA 



XXIX. Spreta. 

 XXX. Lanuginosa. 



XXXII. Sphaerocarpa 



XXXVI. Scoparia. 



XXXVII. Commutata 



XXXVIII. Latipoua. 



XXXI. COLUMBIAN A 



XXXIII. Ensifoua. 



