26bb. CAREX Linnaeus sect. LAXIFLORAE (Kunth) Mackenzie in N. L. Britton et al., N. Amer. Fl. 18: 244. 1935.
Charles T. Bryson & Robert F. C. Naczi
Carex [unranked] Laxiflorae Kunth, Enum. Pl. 2: 452. 1837
Plants usually densely cespitose, short to long rhizomatous. Culms solitary or not, brown or purple at base. Leaves: basal sheaths not fibrous; sheath fronts membranous; blades usually M-shaped in cross section when young, adaxial side of blades with 2 lateral veins more prominent than midvein, widest leaf blades 5+ mm, glabrous. Inflorescences racemose, with 3–6 spikes; proximal nonbasal bracts leaflike, long-sheathing, more than 4 mm, longer than diameter of stem; lateral spikes pistillate, rarely basal, pedunculate, prophyllate; terminal spike staminate. Proximal pistillate scales with apex obtuse, acute, or awned. Perigynia ascending, yellow-brown, to dark brown when mature, not black-mottled, distinctly 8-veined or more, stipitate, obovate to narrowly obovate, trigonous to rounded-trigonous in cross section, base tapering, apex tapering to rounded, abruptly or gradually beak, smooth, glabrous; beak 0.1–1.8 mm, usually more than 5 mm, orifice entire. Stigmas 3. Achenes trigonous; style deciduous.
Species 16 (15 in the flora): North America, Central America.
Carex sect. Laxiflorae is a monophyletic section diagnosed by at least two apomorphies: acute culm angles and epidermal cells of the culms conspicously larger than underlying cells (R. F. C. Naczi 1992). Recent phylogenetic analyses indicate Carex sect. Laxiflorae is a sister group of a clade composed of Carex sects. Granulares, Careyanae, and Griseae (R. F. C. Naczi 1992; R. F. C. Naczi et al. 2002). Eight species formerly included in sect. Laxiflorae in most of the botanical literature have been segregated into sect. Careyanae.
Complete, ample specimens bearing mature perigynia are necessary for identification. Magnification of 10X and bright illumination should be used when examining basal sheaths for presence or absence of purplish coloration, because the coloration is often limited to small areas at the very bases of the plants. When measuring width of the perigynium, care should be taken to measure a perigynium at its widest point, as one face of a perigynium is usually slightly wider than the other two. When measuring length of the peduncle of lateral spike, include the portion of the peduncle enclosed in the bract sheath.
Bryson, C. T. 1980. A Revision of the North American Carex Sect. Laxiflorae (Cyperaceae). Ph.D. dissertation. Mississippi State University