Carex sect. Divisae
in H. G. A. Engler, Pflanzenr. 20[IV,38]: 119. 1909.
Plants not cespitose, sometimes colonial, long-rhizomatous; rhizomes with tight cortex, not detaching on drying, mostly more than 1 mm wide, covered with persistant scales. Culms brown at base, rough, scabrous-angled distally or not. Leaves: basal sheaths fibrous or not; sheath fronts membranous, with hyaline band; blades V-shaped in cross section when young or involute, widest leaves 1+ mm wide, glabrous. Inflorescences racemose, with 3–25+ spikes, ovoid to cylindric, often very condensed; proximal bracts scalelike or cuspidate, or absent, sheathless; spikes staminate, pistillate, or, sometimes, androgynous, sessile, without prophylls. Proximal pistillate scales with apex acuminate, cuspidate, or short-awned. Perigynia ascending to erect, both faces veined or veinless adaxially, often stipitate, ovate to narrowly ovate, plano-convex or biconvex, base rounded, ± spongy, margins acutely angled, apex tapering or contracted to beak, glabrous; beak 0.25–1.9 mm, at least 1/4 length of body, with abaxial suture, margins often serrulate, apex slightly bidentate. Stigmas 2. Achenes biconvex, smaller than bodies of perigynia; style deciduous.
North America, South America, Eurasia, South Africa, Australia.
Species 14 (6 in the flora).
The key to species in sect. Divisae integrates both pistillate and staminate features, but staminate specimens of the section can be more difficult to determine than pistillate ones, especially if the anthers have shed. Staminate culms are usually taller at flowering time than pistillate culms and often conspicuous because of their yellow anthers.
Two types of rhizomes exist in the section. Rhizomes of Carex douglasii, C. duriuscula, and the Eurasian C. stenophylla are slender and terminate in a shoot or more often a cluster of shoots and do not produce shoots regularly along their length. Rhizomes of all other species are coarse, thick, and long creeping and form lines of shoots regularly along their entire length. Eurasian species with slender rhizomes also differ from most other species in the section in all having androgynous spikes and conspicuously spongy-based perigynia and occurring in dryland habitats. T. V. Egorova (1999) placed these species with slender rhizomes onto their own section, Boernera. Carex douglasii, however, is intermediate in some features, having unisexual inflorescences and perigynia not or little spongy-based, and frequently occurring in wetland habitats. One species, C. chordorrhiza, placed by Egorova in the section is excluded here because it has a dramatically different growth form with noncreeping rhizomes and elongate, leafy vegetative culms that become prostrate and root at the nodes.
|1||Culm angles smooth distally; inflorescences usually dense and headlike, usually 1/2+ as wide as long (if pistillate); rhizomes slender, 0.6–1.9 mm thick, shoots often arising 2–several in a cluster and many nodes without shoots.||> 2|
|1||Culm angles at least slightly scabrous distally; inflorescences various; rhizomes coarse, (1.5–)1.8–3.5 mm thick, typically with long, unbranched segments from which shoots arise singly every few nodes.||> 3|
|2||Pistillate scales (4.3–)4.7–7.5 mm, pale brown to ± whitish hyaline; spikes 6–20(–25), usually entirely unisexual; perigynia (3–)3.5–4.2(–4.8) mm; beak (0.9–)1.2–1.9 mm; anthers (2.5–)2.8–3.9 mm, apiculus bristly (30X).||Carex douglasii|
|2||Pistillate scales 2.4–4.1 mm, reddish brown; spikes 3–8, androgynous; perigynia 2.4–3.9 mm; beak 0.3–0.9 mm; anthers 1.4–3 mm, apiculus smooth to warty, very short and broad (30X).||Carex duriuscula|
|3||Perigynium beak 0.25–0.5 mm; apex of inner band of leaf sheath prolonged beyond 0.3–1.6 mm beyond base of blade; anther apiculus smooth to warty (30X).||Carex simulata|
|3||Perigynium beak 0.5–1.5 mm; apex of inner band of leaf sheath not prolonged beyond base of blade; anther apiculus bristly hairy (30X).||> 4|
|4||Scales and spike bracts, at least at base, dark brown or purple-brown, very shiny, darker than the perigynia; inflorescences, if pistillate, compact and broadly ovoid; Pacific Northwest.||Carex pansa|
|4||Scales and spike bracts brown to pale yellowish to reddish brown, ± dull, same color as or lighter than perigynia; inflorescences usually elongate, ellipsoid to narrowly ovoid; not restricted to Pacific Northwest.||> 5|
|5||Perigynium beak 1/4–1/2 length of body; spikes mostly 5–18, mostly entirely pistillate or staminate; widespread, largely western.||Carex praegracilis|
|5||Perigynium beak 1/5–1/4 length of body; spikes mostly 3–10, androgynous; rare introduction along east coast.||Carex divisa|