26xx. CAREX Linnaeus sect. CERATOCYSTIS Dumortier, Fl. Belg. 147. 1827.
William J. Crins
Plants cespitose or not, short-rhizomatous. Culms brown at base. Leaves: basal sheaths not fibrous; sheath fronts membranous; blades sparsely septate-nodulose, usually V-shaped in cross section when young, glabrous. Inflorescences racemose, with 2–6 spikes; proximal nonbasal bracts leaflike, long-sheathing, shorter or longer than diameter of stem; lateral spikes pistillate, rarely distal androgynous, larger spikes with not more than 40 perigynia, dense, pedunculate, prophyllate; terminal spike staminate or, occasionally, androgynous. Proximal pistillate scales with apex obtuse, acute, or cuspidate. Perigynia ascending, spreading, or reflexed, proximal and middle perigyinia separated by internodes less than 1/10 their length, yellow-brown to brown, strongly veined on faces, slightly stipitate, obovoid or, rarely, narrowly ovoid, rounded-trigonous, less than 10 mm, base tapering to rounded, apex abruptly contracted or, rarely, tapering to beak, glabrous; beak bidentate, teeth less than 0.5 mm. Stigmas 3. Achenes trigonous, 1–2 mm, smaller than bodies of perigynia; style deciduous.
Species 7 (5 in the flora): circumboreal, north and south temperate regions in North America, Europe, Asia, Australia.
Sterile hybrids regularly form among species of Carex sect. Ceratocystis. These include Carex hostiana × C. flava (= C. ×xanthocarpa Dégland), C. hostiana × C. viridula (= C. ×fulva Goodenough), C. flava × C. viridula (= C. ×ruedtii Kneucker), and C. cryptolepis × C. viridula.
Some taxa included within C. viridula have been treated as species. Hybrids that form among these taxa (subspecies and varieties) are partially fertile, indicating that they have not diverged widely enough to be reproductively isolated. Their morphologic variation patterns also overlap (W. J. Crins and P. W. Ball 1989).
Carex sect. Ceratocystis is most closely related to sect. Spirostachyae (Drejer) L. H. Bailey, an Old World group with three introduced species in North America. These sections often have been combined as sect. Extensae Fries (a later name), but several characteristics distinguish the sections (W. J. Crins and P. W. Ball 1988).
In the keys that follow, curvature of the perigynium beak is measured as the angle formed by the junction of a straight line through the beak with a straight line through the abaxial portion of the perigynium body. Perigynium length includes the body and beak, unless noted otherwise.
Crins, W. J. and P. W. Ball. 1988. Sectional limits and phylogenetic considerations in Carex section Ceratocystis (Cyperaceae). Brittonia 40: 38–47. Crins, W. J. and P. W. Ball. 1989. Taxonomy of the Carex flava complex (Cyperaceae) in North America and northern Eurasia. II. Taxonomic treatment. Canad. J. Bot. 67: 1048–1065.