2. Chasmanthium laxum (L.) H.O. Yates (spike grass)

Pl. 141 d–g; Map 571

Uniola laxa (L.) Britton, Sterns, & Poggenb.

Plants with short rhizomes, forming clumps. Flowering stems 50–150 cm long, glabrous or somewhat hairy at the nodes. Leaf blades 15–40 cm long, 3–12 mm wide, glabrous or sparsely hairy on the upper surface. Leaf sheaths glabrous to densely hairy. Inflorescences narrow panicles with the branches erect or ascending. Spikelets 5–18 mm long, short‑stalked to nearly sessile, broadly obovate to obtriangular in outline, with 3–7 florets. Glumes 1–3 mm long, narrowly lanceolate to triangular, 3–7‑nerved. Lemmas 3–5 mm long, those of the sterile floret(s) similar to the glumes, those of the fertile florets narrowly oblong‑elliptic, tapered to the narrowly pointed, often inwardly curved tip, 5–7(–9)‑nerved. Stamens with the anther 1.5–2.0 mm long, reddish purple. Fruits 2–3 mm long, exposed and causing the lemma and palea to spread widely at maturity. 2n=24. July–October.

Uncommon in the Mississippi Lowlands Division and St. Louis County (southeastern U.S. west to Oklahoma and Texas). Bottomland forests and mesic upland forests, in sand.

The two subspecies treated below were separated as closely related species by most earlier authors, until Clark (1990) discussed the broad geographical and morphological overlap between them.