10a. var. dichotomum

Pl. 164 i, j

P. dichotomum var. barbulatum (Michx.) A.W. Wood

Main stems with the nodes glabrous or bearded with spreading to downwardly pointed hairs. Leaf sheaths glabrous or the lowermost sparsely to moderately hairy. Leaf blades relatively narrow, those of the leaves toward the middle of the main stem 3–7 mm wide, usually broadest above the base and narrowed somewhat from below the middle, glabrous or the lowermost moderately hairy. Spikelets 1.8–2.3 mm long, rounded at the tip, glabrous or hairy. 2n=18. May–September (vernal), July–November (autumnal).

Common in the Ozark, Ozark Border, and Mississippi Lowlands Divisions, uncommon elsewhere in the state (eastern U.S. and adjacent Canada west to Minnesota and Texas; Mexico). Mesic to dry upland forests, ledges of bluffs, and glades, often on rocky slopes; less commonly acid seeps, fens, and margins of ponds and lakes; also old fields, roadsides, railroads, and open, dry, disturbed areas.

A recent collection from Carter County represents a putative hybrid between the morphologically dissimilar P. dichotomum and P. linearifolium. The specimen originated from a mixed population of the potential parents in an open, dry, upland forest on a south‑facing cherty slope. It has the flowering stems with relatively long, narrow (2.0–4.5 mm wide, more than 20 times as long as wide) leaf blades and inflorescences with ascending branches, as in P. linearifolium, but bearded nodes and relatively small spikelets, as in P. dichotomum. The basal leaves are irregular in length, but relatively narrow, and the leaves of the flowering stems are irregularly and widely spaced and not clustered near the base. The spikelets are not mature enough to have produced fruits and examination of the stamens has been inconclusive, so whether the plants are sterile cannot be determined. Shinners (1944) and Lelong (1965) have discussed the occasional appearance of apparently sterile plants of intermediate morphology in mixed populations of morphologically dissimilar species of Panicum subgenus Dichanthelium. Further hybrids are to be expected uncommonly in Missouri.