Carex sect. Acrocystis
Fl. Belg., 147. 1827.
Plants loosely or densely cespitose, very short to long rhizomatous, stoloniferous. Culms red or brown at base, shorter than leaves. Leaves: basal sheaths fibrous; sheath fronts membranous, mouth ciliate; blades V-shaped in cross section when young, adaxial surface without 2 marginal veins more prominent than midvein, blade 2+ cm, longer than its sheath, 2–4.5 mm wide, glabrous. Inflorescences racemose, with 2–6 spikes; proximal nonbasal bracts filiform or scalelike, sheathless, abaxial surface smooth; lateral spikes pistillate or, rarely, gynecandrous or staminate, sometimes some basal, pedunculate, prophyllate; terminal spike staminate. Proximal pistillate scales white-hyaline or red-brown, 1–3-veined, apex obtuse to acuminate or cuspidate, rarely awned. Perigynia ascending, veined or veinless except for 2 strong marginal veins, stipitate, elliptic or ovate to orbiculate, round or rounded-trigonous in cross section, less than 10 mm, base tapering or rounded, often spongy, apex usually abruptly beaked, pubescent, rarely glabrous; beak straight or bent, 0.5–2.3 mm, bidentate, teeth 0.2–0.5 mm. Stigmas (2–)3. Achenes trigonous, rarely biconvex, almost as large as bodies of perigynia; style deciduous.
Circumtemperate and circumboreal.
Species ca. 35 (20 in the flora).
Carex sect. Acrocystis is well known to be taxonomically difficult, and several complexes require further study, including the Carex umbellata-C. tonsa, the C. deflexa-C. rossii, and the C. geophila-C. pityophila groups. Range extensions and morphologically unusual plants continue to be discovered in areas such as the southern Appalachian Mountains, southeastern coastal plain, and western mountains. More intensive searching may reveal additional range extensions and perhaps also additional new taxa (see C. deflexa).
In the key that follows, perigynia from pistillate spikes at distal cauline nodes of stems with both staminate and pistillate spikes should be selected for measurement. Perigynia from pistillate spikes arising at basal nodes appear to exhibit much more variation in all dimensions, both within and among plants.
Some of the vegetative characters that help to distinguish taxa in the section, such as intact stem bases and rhizomes, are infrequently collected. Such incomplete specimens may be difficult to identify, especially if the inflorescences are immature or over-mature.
Some species in the section may rarely produce unisexual plants or culms (e.g., Carex communis, C. pensylvanica, C. turbinata). Only one species, C. serpenticola Zika, a serpentine endemic from the Klamath Mountains of Oregon and California, produces unisexual culms frequently.
Another potential source of difficulty in identification is caused by putative hybrids between one species that does and one species that does not produce pistillate spikes from basal nodes. Such hybrids have basal pistillate spikes on usually long, filiform peduncles, otherwise they resemble species lacking these basal peduncles. These putative hybrids, which appear to be sterile, have not been studied closely. Parentage of these hybrids is uncertain; they are thought to be derived from Carex peckii or C. pensylvanica and either C. tonsa or C. umbellata.
|1||Inflorescences usually with either staminate or pistillate spikes, not both.||Carex serpenticola|
|1||Inflorescences usually with both staminate and pistillate spikes.||> 2|
|2||Pistillate spikes from basal nodes and cauline nodes in close proximity to staminate spike.||> 3|
|2||Pistillate spikes produced only at cauline nodes in close proximity to staminate spike.||> 11|
|3||Perigynia conspicuously several-veined to at least mid body.||> 4|
|3||Perigynia with 2 main veins, otherwise veinless or with poorly developed, inconspicuous veins near base only.||> 5|
|4||Pistillate scales purplish brown or reddish brown, apex obtuse to cuspidate; perigynium body globose to obovoid; terminal staminate spikes 10–25 mm; basal pistillate spikes on slender, elongate, arching peduncles; leaf blades bright green.||Carex globosa|
|4||Pistillate scales reddish brown, apex cuspidate to acuminate; perigynium body ellipsoid; terminal staminate spikes 5.8–12.7 mm; basal pistillate spikes on stout, short, erect peduncles; leaf blades pale green or glaucous.||Carex brainerdii|
|5||Bracts of the proximal nonbasal pistillate spikes leaflike, equaling or exceeding inflorescences; remnants of old leaves not, or only slightly, shredded into fibers; pistillate scales with apex obtuse, acute, or acuminate, shorter than perigynia.||> 6|
|5||Bracts of the proximal nonbasal pistillate spikes scalelike, usually shorter than inflorescences; remnants of old leaves persisting as tufts of stiff fibers; pistillate scales with apex acute to acuminate, equaling or exceeding perigynia.||> 8|
|6||Rhizomes slender; culms usually loosely cespitose, arching or spreading, smooth except near inflorescence; perigynia 2.3–3.1 mm; beak 0.4–0.8 mm, apical teeth 0.1–0.2 mm; staminate spikes 3.1–11.3 mm.||Carex deflexa|
|6||Rhizomes stout; culms densely cespitose, ascending, scabrous; perigynia 3.1–4.5 mm; beak 0.7–1.7 mm, apical teeth 0.2–0.4 mm; staminate spikes 4.8–12.8 mm.||> 7|
|7||Cauline pistillate spikes 3–15-flowered; margins of perigynium beak ciliate-serrulate; culms 7–30(–40) cm; staminate spikes (4.8–)6–12.8 mm.||Carex rossii|
|7||Cauline pistillate spikes 1–3-flowered; margins of perigynium beak smooth or weakly ciliate-serrulate; culms 3–12 cm; staminate spikes 4.8–5.7(–8) mm.||Carex pityophila|
|8||Perigynia 1.5–2.1 mm wide, round in cross section; beak not strongly 2-edged.||> 9|
|8||Perigynia 1–1.6 mm wide, obtusely trigonous in cross section, beak strongly 2 edged.||> 10|
|9||Cauline pistillate spikes with 5–15 perigynia; culms strongly fibrous at base.||Carex geophila|
|9||Cauline pistillate spikes with 1–6 perigynia; culms slightly fibrous at base.||Carex brevicaulis|
|10||Perigynia 2.2–3.2 × 1–1.4 mm; beak 0.4–1 mm.||Carex umbellata|
|10||Perigynia 3.1–4.7 × 1.1–1.6 mm; beak 0.9–2 mm.||Carex tonsa|
|11||Perigynium body globose to obovoid, about as long as wide.||> 12|
|11||Perigynium body ellipsoid, longer than wide.||> 17|
|12||Plants densely cespitose; rhizomes short, not horizontally spreading or absent; widest leaves 3+ mm wide; staminate spikes 1–2.5 mm wide.||Carex communis|
|12||Plants loosely cespitose or with solitary stems; rhizomes long, horizontally spreading (except in C. turbinata); widest leaves usually less than 3 mm wide; staminate spikes usually more than 2 mm wide.||> 13|
|13||Perigynia 10–25-veined to at least mid body; rhizomes short, ascending or absent.||Carex turbinata|
|13||Perigynia usuallly veinless except for 2 strong marginal veins running length of body and beak; rhizomes long, horizontally spreading.||> 14|
|14||Perigynia 1.5–2.3 mm wide; achenes (1.4–)2.1–2.5 mm.||> 15|
|14||Perigynia 1.1–1.5(–1.7) mm wide; achenes 1.3–1.9(–2.3) mm.||> 16|
|15||Scales and bases of proximal cauline bracts green or reddish brown; pistillate scales and proximal staminate scales with conspicuous white margins 0.4–0.8 mm wide.||Carex inops|
|15||Scales and bases of proximal cauline bracts dark purple to black; pistillate scales and proximal staminate scales with narrow white margins 0.1–0.2 mm wide.||Carex serpenticola|
|16||Beaks of perigynia 0.5–0.9 mm; blades of distal cauline leaves well developed; culms usually smooth or weakly scabrous distally.||Carex pensylvanica|
|16||Beaks of perigynia 0.9–1.6 mm; blades of distal cauline leaves poorly developed; culms usually strongly scabrous distally.||Carex lucorum|
|17||Widest leaves 3+ mm wide; pistillate spikes and staminate spike not closely aggregated, usually clearly separated.||Carex communis|
|17||Widest leaves 3.3 mm wide or less, if leaves more than 2.9 mm wide, then pistillate spikes closely aggregated with each other and with staminate spike.||> 18|
|18||Proximal 2 pistillate spikes usually separated by more than 7 mm, remote, not overlapping; proximal cauline bracts equaling or exceeding inflorescences.||Carex novae-angliae|
|18||Proximal 2 pistillate spikes contiguous or overlapping, usually separated by less than 7 mm; proximal nonbasal bracts shorter than inflorescences.||> 19|
|19||Pistillate scales shorter than perigynia, perigynia conspicuous among scales.||> 20|
|19||Pistillate scales about as long as perigynia, perigynia nearly or completely concealed.||> 21|
|20||Perigynia 2.3–3.1 mm; culms slender, 5–31 cm; leaves usually equaling or longer than culms.||Carex deflexa|
|20||Perigynia 3.2–4.2 mm; culms more robust, 21–47 cm; leaves shorter than culms.||Carex peckii|
|21||Culms 10–45 cm, usually more than 20 cm; bases (remnants of old leaves) slightly or not at all fibrous; staminate peduncles 0.4–9.9 mm.||Carex albicans|
|21||Culms 2–27 cm, usually less than 20 cm; bases (remnants of old leaves) slightly to strongly fibrous; staminate peduncles 0.3–1.2 mm.||> 22|
|22||Rhizomes ascending to erect, 0–10 mm; stigmas 3; achenes obtusely trigonous in cross section; culm bases often strongly fibrous.||Carex nigromarginata|
|22||Rhizomes horizontally spreading to ascending, 17–75 mm; stigmas 2 or 3; some achenes biconvex or trigonous; culm bases usually weakly fibrous.||Carex floridana|