Plants usually densely cespitose. Basal rosettes well-differentiated; blades 1.5-6 cm, ovate to lanceolate. Culms 15-50 cm, slender, wiry; internodes olive green to purplish, densely puberulent or glabrous; fall phase spreading or decumbent, branching extensively from the lower and midculm nodes, producing numerous congested fascicles of reduced, flat or involute blades and reduced secondary panicles. Cauline leaves 4-7; sheaths much shorter than the internodes, densely crisp-puberulent, velvety-puberulent, or glabrous, often ciliate along the margins; ligules shorter than 0.5 mm; blades 2-7 cm long (seldom longer), 2.5-8 mm wide (rarely wider), spreading, firm, flat or slightly involute, without prominently raised veins, not longitudinally wrinkled, densely puberulent or glabrous abaxially, glabrous, sparsely puberulent, or pubescent adaxially, bases subcordate, with papillose-based cilia, margins often whitish and scabridulous. Primary panicles 2-7 cm long, 2/3 to nearly as wide as long, with relatively few spikelets, exserted; branches flexuous, spreading or reflexed, scabridulous to densely puberulent. Spikelets 1.5-2.6 mm, obovoid-pyriform, planoconvex in side view, puberulent, pubescent, or glabrous, attenuate basally, apices usually broadly rounded. Lower glumes 0.6-1.4 mm, thin, weakly-veined, attached about 0.2 mm below the upper glumes, clasping at the base; upper glumes as long as or slightly shorter than the lower lemmas; upper florets 1.4-2 mm, broadly ellipsoid, apices subacute, minutely puberulent. 2n = 18.

Dichanthelium portoricense grows in sandy woods, low pinelands, savannahs, and coastal sand dunes, usually in moist places. Its range extends south from the Flora region into Mexico, the Caribbean, and Mesoamerica. It is a highly variable species with numerous intergrading forms, some possibly resulting from hybridization with other widespread species in the same region, such as D. sphaerocarpon and D. commutatum.

Culms 20-50 cm, often densely puberulent. Sheaths puberulent to subglabrous. Cauline blades 4-7 cm long, 3.5-8 mm wide. Primary panicles 2-7 cm. Spikelets 1.8-2.6 mm, usually densely pubescent or puberulent, rarely glabrous.

Dichanthelium portoricense subsp. patulum is more common in moist, sandy pinelands and savannahs than subsp. portoricense. It also grows in coastal sand dunes, but is less abundant there than subsp. portoricense. It is the more variable of the two subspecies, grading into subsp. portoricense as well as D. commutatum. More robust plants are recognized by some as Panicum patentifolium Nash. Occasional specimens, recognized by some as P. webberianum Nash, resemble the widespread D. sphaerocarpon.

Culms 15-40 cm, glabrous or puberulent. Sheaths glabrous or puberulent; cauline blades 2-5 cm long, 2.5-4.5 mm wide, usually puberulent abaxially and glabrous adaxially. Primary panicles 2-4.5 cm. Spikelets 1.5-2.0 mm, puberulent to nearly glabrous.

Dichanthelium portoricense subsp. portoricense is more common than subsp. patulum in coastal sand dunes. It also grows in sandy pinelands and savannahs. It resembles D. aciculare somewhat, but that species usually has ascending-pilose culms, strongly involute or acicular blades, and longer spikelets.