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, yellowbrown 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.
Distribution
Circumboreal, north and south temperate regions in North America, Europe, Asia, Australia
Discussion
Species 7 (5 in the flora).
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.
Selected References
None.
Lower Taxa
Key
| 1 | Plants not cespitose, with short, stout, horizontal rhizomes; inner band of bract sheaths with convex projections to 3.2 mm; scales dark brown with conspicuous white borders; perigynia ascending. | Carex hostiana |
| 1 | Plants cespitose; inner band of bract sheaths truncate or concave; scales yellowish green to reddish brown with inconspicuous hyaline borders; perigynia (in fruit) spreading or reflexed. | > 2 |
| 2 | Perigynia spreading; beak straight or forming angle less than 25° with body; ligules on distal cauline leaves usually obsolete. | Carex viridula |
| 2 | Proximal perigynia reflexed; perigynium beak forming angle usually greater than 20° with body; ligules on distal cauline leaves truncate or rounded, well developed. | > 3 |
| 3 | Pistillate scales yellowish green, similar in color to perigynia. | > 4 |
| 3 | Pistillate scales brownish, contrasting with yellowish green perigynia. | > 5 |
| 4 | Tallest culms 25–50 cm; proximal pistillate spike bracts 1.5–4 times as long as inflorescences; peduncles of staminate spikes 0.2–0.5 length of staminate spikes; perigynium beak smooth; achenes 1–1.2 mm wide. | Carex cryptolepis |
| 4 | Tallest culms 65–125 cm; proximal pistillate spike bracts 0.5–1.3(–1.9) times as long as inflorescences; peduncles of staminate spikes mostly 0.7–2.5 length of staminate spikes; perigynium beak usually sparsely scabrous; achenes 1.2– 1.5 mm wide. | Carex lutea |
| 5 | Staminate spikes sessile or short-pedunculate, peduncles usually less than 5 mm; cauline leaves usually nearly as long as culms; perigynium beak conspicuously scabrous, usually more than 1.6 mm. | Carex flava |
| 5 | Staminate spikes on peduncles usually more than 4.5 mm; cauline leaves 0.5 times as long as culms or less; perigynium beak weakly scabrous, usually less than 1.7 mm. | Carex viridula |
"shortened" is not a number.