GRAMINEAE (GRASS FAMILY) 



155 



Annuals. 



Florets not webby at the base ; lemmas distinctly 5-nerved 

 Florets webby at the base ; intermediate pair of nerves obscure . 

 Perennials. 

 Culms from extensively creeping rootstocks, not tufted. 



Culms flattened ; spikelets not over 6 mm. long 



Culms terete ; spikelets 8 mm. or more long 



Culms tufted. 



Creeping rootstocks present. 



Panicle crowded ; culms much exceeding the leaves . * . * 

 Panicle diffuse ; culms scarcely exceeding the basal leaves 

 No creeping rootstocks, but culms sometimes decumbent at base. 



Lemma glabrous 



Lemma pubescent at least on the keel. 



Culms upright from a stout crown or caudex ; leaves short and flat 

 Culms from a more slender base forming loose tufts, often decum- 

 bent. 



Culms rarely over 3 dm. high, with lax leaves, the decumbent 

 bases of the culms forming loose tufts ; lemma pubescent 

 but very sparsely webbed ; alpine or northern plants . 

 Culms taller, or if low, stiff and with scarcely decumbent bases. 

 Lemma not webbed at base. 



Panicle narrow ; lemma glabrous between the nerves below 

 Panicle spreading : lemma pubescent between the nerves 



below 



Lemma webbed at base. 

 Marginal nerves glabrous. 



Lemma prominently nerved ; sheaths scabrous. 

 Lemma obscurely nerved ; sheaths smooth 

 Marginal nerves pubescent. 



Intermediate nerves of lemma obscure ; florets acute. 

 Panicle erect, 0.4-1 dm. long (rarely longer), branches 



ascending 



Panicle drooping, 1-3 dm. long, branches spreading 

 Intermediate nerves of lemma prominent ; florets obtuse 



or acutish. 

 Branches of panicle spikelet-bearing from the middle ; 



spikelets 3-4 rnm. long 



Branches of panicle elongated, spikelet-bearing only at 

 the ends ; spikelets 5-6 mm. long .... 



1. P. annua. 



2. P. Chapmaniana. 



3. P. compressa. 



4. P. eminens. 



10. P. pratensis. 



17. P. brachyphylla. 



18. P. debilis. 

 5. P. alpina. 



6. P. laasa. 



7. P. glauca. 



16. P. autumnalis. 



11. P. trivialia. 

 14. P. alsodes. 



8. P. nemoralia. 



9. P. triflora. 



12. P. 

 15. P. 



* Annuals, rarely over 2.5 dm. high, tufted. 



1. P. ANNUA L. (Low SPEAR GRASS.) Culms flattened, decumbent at base, 

 sometimes rooting at the lower nodes ; sheaths loose ; leaves very soft ; panicle 

 pyramidal, 3-8 cm. long, rarely longer; spikelets crowded, 3-6-flowered, about 

 4mm. long ; lemma distinctly b-nerved, the nerves hairy below. Cultivated and 

 waste grounds, everywhere. Apr.-Oct. (Nat. from Eu.) 



2. P. Chapmaniana Scribn. Similar to the preceding but more strict in 

 habit ; culms terete, erect ; sheaths close, mostly at the base ; panicle more 

 oblong; florets webbed at the base, the intermediate nerves of lemmas very 

 obscure, the middle and marginal nerves sometimes hairy below. Dry soil, 

 Va. to s. 111., and south w. Apr., May. 



* * Perennials. 

 H- Culms from extensively creeping rootstocks, not tufted. 



3. P. COMPRESSA L. (CANADA BLUE GRASS. WIRE 



GRASS.) Bluish-green, 2-6 dm. high; culms geniculate- 

 ascending, wiry, flattened ; panicles 2-8 cm. long, narrow, 

 the usually short branches in pairs, spikelet-bearing to the 

 base ; spikelets crowded, subsessile, 3-6(rarely 9)-flowered, 

 4-6 mm. long ; lemmas obscurely nerved, more or less bronzed 

 at the summit. Dry mostly sterile soil, Nfd. to S. C., and 

 westw. ; also cultivated as a pasture grass. May-Sept. (Nat. 

 from Eu.) FIG. 163. 



4. P. Iminens J. S. Presl. Glaucous, glabrous, 3-9 dm. 

 high ; culms stout, erect, terete ; sheaths overlapping, clus- 

 tered on the sterile shoots ; blades thick, 3-8 mm. wide ; p anic i e x i/ 4 . 

 panicle heavy, 8-16 cm. long, contracted ; spikelets 3-5-flow- spikelet and floret x 2. 

 ered, 8-12 mm. long; lemmas 4-5 mm. long, distinctly Lemma x 8. 



P. compressa. 



