Digitaria

The first glume is minute, sometimes membranous or apparently absent.

1. Inflorescence an open panicle, neither spike-like nor distinctly one-sided.

D. cognata

1. Inflorescence composed of 1-sided spikes or spike-like racemes, the rachis of each winged or at least flat on the side opposite the spikelets.

2. Rachis of racemes scarcely if at all winged; culms erect, not rooting at lower nodes.

D. filiformis

2. Rachis of racemes distinctly winged (wing broader than rachis proper); culms usually ± decumbent at base, often rooting at lower nodes.

3. Spikelets ca. (1.7–) 2–2.3 mm long, the fertile lemma dark brown; second glume nearly or fully as long as the floret; sheaths and blades usually nearly or quite glabrous (except around summit of sheath).

D. ischaemum

3. Spikelets ca. 2.5–3 mm long, the fertile lemma light or dark grayish; second glume only about half as long as the floret; sheaths and usually blades ± pilose, at least toward base of plant.

D. sanguinalis

All species found in Digitaria

Digitaria cognataFALL WITCH GRASS 
Digitaria filiformisSLENDER CRAB GRASS 
Digitaria ischaemumSMOOTH CRAB GRASS 
Digitaria sanguinalisHAIRY CRAB GRASS 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. November 22, 2017. http://michiganflora.net/genus.aspx?id=Digitaria.