Plants annual, or short-lived perennials; cespitose, not rhizomatous.
Culms (10)25-150 cm, erect or decumbent, branching, sometimes rooting
at the lower nodes; nodes 3-6. Sheaths keeled, basal sheaths usually
with papillose-based hairs, rarely glabrous; ligules 0.3-1.5 mm; blades
2-18 cm long, 1-6 mm wide, flat or involute, glabrous, scabrous, or pilose.
Panicles with 2-7 spikelike primary branches, these digitate or the rachises
to 1 cm; longest primary branches 3-25 cm long, 0.2-0.4 mm wide, axes
triquetrous, not wing-margined, with spikelets in groups of 2-5 on the lower
and middle portions. Spikelets 1.3-2.8 mm. Lower glumes absent
or to 0.1 mm; upper glumes 1-2 mm long, from 3/4 to almost as long as
the spikelets, almost glabrous or sparsely to densely pubescent with clavate
to capitate hairs (use 20× magnification), glume apices rounded; lower
lemmas equaling the spikelets, glabrous or glandular-pubescent, 5-7-veined,
veins unequally spaced, outer 3 veins on each side closer to each other than
the midvein is to the inner lateral veins; upper lemmas 1.3-2 mm, apiculate,
dark brown at maturity; anthers 0.3-0.6 mm. 2n = 36, 54.
Digitaria filiformis grows throughout the warmer parts of the eastern
United States. Digitaria filiformis var. filiformis, the most widespread
of its varieties, extending into Mexico.
Branched from the base, erect or ascending; blades 2-6 mm wide, flat, at least the lower commonly pilose; racemes 2-6, erect or ascending, often distinctly separated at base; rachis triquetrous, scarcely winged; spikelets in pairs or threes, well separated and scarcely overlapping; first glume lacking; the second three-fifths to three-fourths as long as the spikelet, usually pubescent and erose-ciliate with capitellate hairs; fertile lemma dark brown or purple; 2n=36. Fields and open ground, often a troublesome weed southward. Forms with glabrous spikelets occur in both vars. (D. laeviglumis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.