MANUAL OF THE GRASSES OF THE UNITED STATES 



553 



and blades nearly glabrous to puberulent, sometimes densely so 

 toward base, the blades 2 to 5 cm long, 2 to 3 mm wide; panicle 

 long-exserted, 6 to 10 cm long, the few racemes 3 to 4 cm long, 

 mostly rather remote and erect; spikelets 2.5 to 3 mm long, densely 

 silky- villous, the prominent nerves not hidden, the grayish hairs 

 not exceeding the spikelet. % — Dry plains, Texas; northern 

 Mexico. 



121. DIGITARIA Heister. Crabgrass 



(Syntherisma Walt.) 



Spikelets in twos or threes, rarely solitary, subsessile or 

 pediceled, alternate in two rows on one side of 

 a 3-angled winged or wingless rachis; spikelets 

 lanceolate or elliptic, nearly planoconvex; first 

 glume minute or wanting; second glume equal- 

 ing the sterile lemma or shorter; fertile lemma 

 cartilaginous, the hyaline margins pale. An- 

 nual or perennial, erect to prostrate, often 

 weedy grasses, the slender racemes digitate or 

 approximate on a short 

 axis. Type species, Digi- 

 taria sanguinalis. Name 

 from Latin digitus, finger, 

 alluding to the digitate 

 inflorescence of the type 

 species. 



The species are in the 

 main good forage grasses. 

 Digitaria sanguinalis, the common crabgrass, is 

 a weed in cultivated soil. In the Southern 

 States, where it produces an abundant growth 

 in the late summer on fields from which crops 

 have been gathered, it is utilized for forage and 

 is sometimes cut for hay. This species and D. 

 ischaemum are common weeds in lawns. They 

 form a fine green growth at first but they start figure 

 late and die in the fall. 



short- 



Figure 1157.— Distribution of 

 Trkhachne californica. 



1156.— Trichachne cali- 



fornica, X 1. 

 13608, Tex.) 



(Hitchcock 



la. Rachis winged or flat-margined, the margin as wide as the central rib; 

 plants annual, creeping at least at base. 

 Rachis bearing scattered long fine hairs (these rarely wanting); spikelets 



narrow, acuminate, nearly glabrous 2. D. horizoxtalis. 



Rachis not bearing hairs; spikelets elliptic, acute, pubescent. 

 Sheaths glabrous; fertile lemma brown. 



Spikelets 2 mm long, 1 mm wide, the hairs or most of them capitellate. 



3. D. ISCHAEMUM. 



Spikelets 1.5 to 1.7 mm long, about 0.6 mm wide, the hairs not capitellate. 



Sterile lemma with 5 distinct nerves; spikelets sparingly pubescent, 



1.7 mm long; fertile lemma light brown; racemes, if more than 



2, not digitate 4. D. florfdaxa. 



Sterile _ lemma with 3 distinct nerves; spikelets distinctly pubescent, 

 1.5 mm long, fertile lemma dark brown, racemes" usually all 



_, digitate 5. D. violascexs. 



Sheaths pilose or villous; fertile lemma pale. 



Spikelets 1.5 to 1.7 mm long; pedicels terete, glabrous.__ 6. D. serotina. 

 Spikelets 2.5 to 3.5 mm long; pedicels angled, scabrous. 



1. D. sanguinalis. 



