22. Panicum portoricense Desv. ex Ham.

Pl. 164 g, h; Map 683

P. columbianum Scribn.

P. acuminatum Sw. var. columbianum (Scribn.) Lelong

Dichanthelium columbianum (Scribn.) Freckmann

D. portoricense (Desv. ex Ham.) B.F. Hansen & Wunderlin

D. sabulorum (Lam.) Gould & C.A. Clark var. thinium (Hitchc. & Chase) Gould & C.A. Clark

Plants perennial, without rhizomes, forming tufts. Flowering stems 10–60 cm long, erect or spreading, initially unbranched, becoming much‑branched during the summer and autumn, the nodes and internodes short‑hairy, the internodes sometimes also with a few scattered, longer hairs. Foliage in a dense rosette of shorter, somewhat broader leaves at the base and longer, narrower leaves well distributed along the main stems, those of the later branches often appearing as axillary fascicles of even shorter, narrower leaves. Leaf sheaths hairy, at least the lowermost sheaths usually with numerous, shorter, stiff, appressed hairs mixed with sparse, longer, softer, spreading hairs, at least some of the hairs with pustular bases, the ligule 0.5–1.5 mm long, an inconspicuous line or band of hairs. Leaf blades of the main stems 1–7 cm long, 3–7 mm wide, abruptly rounded or truncate at the base, relatively thick and stiff, glabrous or sparsely short‑hairy on the upper surface, usually short‑hairy on the undersurface, some of the hairs sometimes with pustular bases, the margins somewhat thickened and with sparse, stiff hairs at the base. Inflorescences 2.5–4.5 cm long, the earlier ones larger and more open with mostly spreading to loosely ascending branches (later ones sometimes reduced to small clusters of long‑stalked spikelets), the branches mostly rebranched 1 or more times, not spikelike or 1‑sided, the spikelets appearing short‑ to long‑stalked at the tips of the branches. Spikelets 1.2–2.0 mm long, broadly elliptic to slightly obovate in outline. Lower glume 0.3–0.6 mm long, 1/4–1/3 as long as the spikelet, broadly ovate, bluntly to sharply pointed at the tip, glabrous or sparsely hairy, nerveless or faintly 1–5‑nerved. Upper glume 1.0–1.8 mm long, broadly elliptic‑obovate, rounded at the tip, 5–9‑nerved, hairy. Lowermost floret sterile and with a reduced, inconspicuous palea, the lemma 1.0–1.8 mm long, broadly elliptic‑obovate, rounded at the tip, 5–9‑nerved, hairy. Fertile floret 1.0–1.6 mm long, elliptic, rounded or bluntly pointed at the tip. Anthers 0.2–0.8 mm long. 2n=18. May–September (vernal), June–November (autumnal).

Uncommon, known presently only from a single collection from Taney County (northeastern U.S. west to Minnesota and Missouri, uncommonly farther south). Savannas, to be expected in mesic to dry upland forests and glades.

This species has a confusing history of treatment, both taxonomically and as part of the Missouri flora. Gould and Clark (1978) treated it as a variety of the South American D. sabulorum, but subsequent authors have argued that the North and South American plants are different species (Lelong, 1984, 1986; Hansen and Wunderlin, 1988). Opinions have varied on the correct name to apply to materials from the United States, but P. portoricense appears to be the oldest epithet that applies to the taxon. In Missouri, Steyermark (1963) excluded the species, based upon uncertain data on the label of the single collection that he thought might represent the taxon. Examination of this specimen during the present study resulted in its redetermination as P. acuminatum var. acuminatum. Nelson (1982) reported P. columbianum for Missouri based on a collection of his from Reynolds County, but that specimen is also P. acuminatum var. acuminatum. Most recently, Doug Ladd collected another specimen of this taxon from Taney County that has been verified as true P. portoricense, and the species is thus reinstated as a part of the Missouri flora.