Carex sect. Laxiflorae
in N. L. Britton et al., N. Amer. Fl. 18: 244. 1935.
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.
North America, Central America.
Species 16 (15 in the flora).
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.
|1||Bract blades of distal lateral spikes lanceolate or narrowly lanceolate, wider than spikes, concealing them (viewed from abaxial surface), widest bract blade of distalmost lateral spike (2.9–)3.2–8.3 mm wide.||> 2|
|1||Bract blades of distal lateral spikes linear, narrower than spikes, not concealing them (viewed from abaxial surface), widest bract blade of distalmost lateral spike 0.5–3.4 mm wide.||> 3|
|2||Widest leaf or bract blade 13–38(–62) mm wide; pistillate scales from proximal portions of spikes truncate, awnless (sometimes mucronate); perigynia 1.8–2.1 mm wide.||Carex albursina|
|2||Widest leaf or bract blade 5.3–11 mm wide; pistillate scales from proximal portions of spikes acute or awned; perigynia 1.3–1.7(–1.8) mm wide.||Carex kraliana|
|3||Perigynia 8–18-veined, 2(–3) veins conspicuous.||Carex leptonervia|
|3||Perigynia (22–)25–32-veined, all veins conspicuous.||> 4|
|4||Basal sheaths purple, reddish purple, or purple tinged.||> 5|
|4||Basal sheaths brownish, not purplish.||> 8|
|5||Perigynia 2.4–3.3 mm.||> 6|
|5||Perigynia 3.4–4.5 mm.||> 7|
|6||Perigynia closely overlapping, 1.8–2.7 times long as wide; beaks 0.2–0.8 mm; internodes in proximalmost spikes 1.1–3.2(–4.8) mm; angles of bract sheaths denticulate.||Carex gracilescens|
|6||Perigynia loosely overlapping or separate, 1.7–2.1 times long as wide; beak 0.1–0.3 mm; internodes in proximalmost spikes 3.3–14 mm; angles of bract sheaths smooth or minutely papillose.||Carex ormostachya|
|7||Longest peduncle of terminal spike (0.4–)3.1–5.4(–15.7) cm; terminal spike exceeding bract blade of distalmost lateral spike; blades of overwintered leaves densely papillose abaxially.||Carex purpurifera|
|7||Longest peduncle of terminal spike (0.9–)1.2–3.2(–5.3) cm; terminal spike usually exceeded by bract blade of distalmost lateral spike; blades of over wintered leaves smooth abaxially.||Carex manhartii|
|8||Perigynia closely overlapping: ratio of longer lateral spike length (in mm) to perigynia number = 0.8–1.7.||> 9|
|8||Perigynia loosely overlapping or separate: ratio of longer lateral spike length (in mm)/perigynia number = 1.9–3.4.||> 12|
|9||Perigynia 2.5–3.8(–4.1) mm, 1.5–1.9 times as long as achene bodies; beak 0.2–0.6 mm.||Carex blanda|
|9||Perigynia (3.3–)3.9–5.5 mm, 1.9–2.3 times as long as achene bodies; beak 0.5–1.7 mm.||> 10|
|10||Distal lateral spikes overlapping; terminal spike exceeded by or subequal to distal lateral spike; perigynia ascending; peduncle of proximalmost spike arising in distal 1/2 of culm.||Carex crebriflora|
|10||Distal lateral spikes separate; terminal spike clearly exceeding distal lateral spike; perigynia spreading; peduncle of proximalmost spike arising in proximal 1/3 of culm.||> 11|
|11||Plants densely cespitose, short-rhizomatous.||Carex styloflexa|
|11||Plants loosely cespitose or not cespitose, long-rhizomatous.||Carex chapmanii|
|12||Pistillate scales 1.9–2.3 mm wide.||Carex hendersonii|
|12||Pistillate scales 1.1–1.8 mm wide (to 2.1 mm in C. radfordii, to 2.2 in C. striatula).||> 13|
|13||Longer peduncles of proximal lateral spikes 4.6–14 times as long as spikes they subtend; perigynia spreading.||> 14|
|13||Longer peduncles of proximal lateral spikes 1.4–3.3(–5.3) times as long as spikes they subtend; perigynia ascending.||> 15|
|14||Culms densely tufted.||Carex styloflexa|
|14||Culms loosely tufted or solitary.||Carex chapmanii|
|15||Longest bract blade 5–8 cm; blades of overwintered leaves densely papillose abaxially.||Carex radfordii|
|15||Longest bract blade (4.5–)6.5–15 cm; blades of overwintered leaves usually smooth, rarely, sparsely papillose abaxially.||> 16|
|16||Achenes 1.8–2.2(–3.4) mm; perigynia (2.6–)3.2–4.1(–4.6) mm; terminal spike 12–24(–34) mm.||Carex laxiflora|
|16||Achenes 2.2–2.8(–4.6) mm; perigynia (3.4–)3.9–5.1 mm; terminal spike 22–32(–36) mm.||Carex striatula|