MANUAL OF THE GRASSES OF THE UNITED STATES 



555 



lb. Rachis wingless or with a very narrow margin (see also D. horizontalis) , 

 triangular; plants not creeping (except in D. texana), annual or perennial. 

 2a. Fertile lemma pale or gray. 



Plants annual, decumbent and rooting at base. Spikelets 3 mm long, 



glabrous or nearly so 7. D. simpsoni. 



Plants perennial. 



Spikelets densely or sparsely villous; racemes 5 to 10. 



Spikelets 3. 5 to 4 mm long, sparsely to densely villous- 15. D. runyoni. 



Spikelets 2.3 to 2.8 mm long, rather sparsely villous. _ 12. D. texana. 



Spikelets glabrous to obscurely appressed-pubescent on the internerves; 



racemes 2 to 5, some of them naked at base for 1 to 1.5 cm. 



First glume broad, hyaline, minute but obvious; spikelets 3.2 mm long, 



glabrous 13. D. pauciflora. 



First glume obsolete or nearly so; spikelets 2.5 to 2.8 mm long, obscurely 



to obviously appressed-pubescent 14. D. subcalva. 



2b. Fertile lemma dark brown. Plants erect or at least not rooting at the 

 decumbent base; annual or sometimes apparently perennial. 

 Second glume and sterile lemma glabrous (see also D. laeviglumis under 



D. filiformis) 11. D. gracillima. 



Second glume and sterile lemma capitellate-pubescent. 



Spikelets 2 to 2.5 mm long 9. D. VILLOSA. 



Spikelets 1.5 to 1.7 mm long. 



Blades folded "or involute, flexuous 10. D. panicea. 



Blades flat 8. D. filiformis. 



1. Digitaria sanguinalis (L.) Scop. Crabgrass. (Fig. 1160.) 

 Plant branching and spreading, often purplish, rooting at the decum- 

 bent base, the culms sometimes as much as 1 

 m long, the flowering shoots prostrate or 

 ascending; sheaths, at least the lower, papillose- 

 pilose; blades 5 to 10 mm wide, pubescent to 

 scaberulous; racemes few to several, 5 to 15 cm 

 long, rarely longer, digitate, with usually 1 or 

 2 whorls a short distance below; spikelets 

 about 3 mm long ; first glume minute but evident ; 

 second glume about half as long as the 

 spikelet, narrow, ciliate; sterile lemma strongly 

 nerved, the lateral internerves appressed- 

 pubescent, the hairs sometimes spreading 

 at maturity (D. Jimbriata Link) ; fertile lemma 

 pale, o — Fields, gardens, and waste places, 

 a troublesome weed in cultivated ground, 

 throughout the United States, at low and me- 

 dium altitudes, more common in the East and 

 South; temperate and tropical regions of the 

 world. Native of Europe. A specimen with 

 nearly glabrous sheaths and inflorescences of 

 2 racemes collected by Tracy in Mississippi, 

 said to be introduced, has been erroneously 

 referred to Syntherisma barbatwn (Willd.) Nash 

 (Digitaria barbata Willd.). 



2. Digitaria horizontalis Willd. (Fig. 1161.) 

 Resembling D. sanguinalis but the racemes 

 more slender and lax, rachis scarcely winged, 

 bearing scattered long fine spreading hairs (these rarely wanting); 

 spikelets narrow, about 2 mm long; first glume minute or obsolete; 

 second glume half as long as the spikelet. o (Syntherisma setosum 

 Nash; S. digitatum Hitchc.) — Waste places, southern and central 

 Florida; ballast, Mobile, Ala.; tropical regions of both hemispheres. 



Figuke 1159.— Trichachne hitch- 

 cockii. Plant, X 1; spikelet 

 and floret, X 10. (Type.) 



