Carex
Sp. Pl. 2: 972. 1753.
Gen. Pl. ed. 5, 420. 1754.
Herbs, perennial, cespitose or not, rhizomatous, rarely stoloniferous. Culms usually trigonous, sometimes round. Leaves basal and cauline, sometimes all basal; ligules present; blades flat, V-shaped, or M-shaped in cross-section, rarely filiform, involute, or rounded, commonly less than 20 mm wide, if flat then with distinct midvein. Inflorescences terminal, consisting of spikelets borne in spikes arranged in spikes, racemes, or panicles; bracts subtending spikes leaflike or scalelike; bracts subtending spikelets scalelike, very rarely leaflike. Spikelets 1-flowered; scales 0–1. Flowers unisexual; staminate flowers without scales; pistillate flowers with 1 scale with fused margins (perigynium) enclosing flower, open only at apex; perianth absent; stamens 1–3; styles deciduous or variously persistent, linear, 2–3 (–4) -fid. Achenes biconvex, planoconvex, or trigonous, rarely 4-angled. x = 10.
Contents
- 1 Distribution
- 2 Discussion
- 3 Selected References
- 4 Lower Taxa
- 5 Keys
- 5.1 Key to sections of Carex
- 5.2 Key A. Spike 1 per culm, all flowers attached to main stem in terminal spike.
- 5.3 Key B. Spikes 2+ per culm; all flowers staminate
- 5.4 Key C. Spikes 2+ per culm; at least some flowers pistillate; stigmas 2; achenes flat to biconvex in cross section
- 5.5 Key D. Spikes 2+ per culm; at least some flowers pistillate; stigmas (2–)3(–4); achenes usually trigonous in cross section; body of perigynium pubescent to hispid, sometimes papillose, papillae longer than wide
- 5.6 Key E. Spikes 2+ per culm, at least some flowers pistillate; stigmas (2–)3(–4); achenes usually ± trigonous in cross section; body of perigynium glabrous or papillose, papillae then mostly not longer than wide; bracts sheathless or sheath less than 4 mm, rarely longer, then sheath shorter than diameter of stem
- 5.7 Key F. Spikes 2+ per culm, at least some flowers pistillate; stigmas (2–)3(–4); achenes usually ± trigonous in cross section; body of perigynium glabrous or papillose, papillae mostly not longer than wide; bracts, at least proximal, with sheath 4+ mm, longer than diameter of stem
Distribution
Worldwide
Discussion
Species ca. 2000 (480 in the flora).
Carex is one of the largest genera of vascular plants. Almost worldwide in distribution, it is absent from tropical lowlands except for a few species in southeast Asia. The genus is poorly represented also in sub-Saharan Africa. The flora area is species rich, almost comparable to eastern Asia. Carex is most commonly associated with moist to wet habitats, usually with water not more than 50 cm deep in the growing season. Species of Carex are often dominant or co-dominant in such habitats, including arctic tundra. Carex is often common also in montane grasslands, montane rocky habitats, and forests. In eastern North America, many species occur in deciduous or mixed forests, where they are major constituents of the understory. In eastern forests, 20 or more species of Carex may be found within a few hectares.
All Carex are perennial, but a few species may fruit in their first year and not persist (C. bebbii, C. crawfordii, C. sychnocephala, C. viridula, and no doubt others). A few species, such as C. adusta, are short-lived, with individuals living only three to five years. All species have rhizomes, though in densely cespitose species the rhizomes are often very short and inconspicuous, leading some authors to consider them absent. In some, the rhizomes are elongated, and the plants may form extensive swards. A few species, such as C. stricta and some other tussock forming species and some species that occur on sand dunes, have rhizomes that can grow vertically.
Shoots of sedges vary greatly in their longevity. In many species, all aboveground shoots are annual. In others, individual shoots may live more than one season. In such species, shoots may be vegetative in the first year and flower in a subsequent year. In species with annual flowering stems, only bladelesss basal sheaths occur, clothing the base of the stem. Those stems are termed aphyllopodic (from the absence of leaf blades on the basal sheaths of the stem) or lateral (because they are formed lateral to previous year’s shoot). In species where the flowering stem is produced from the apical meristem of a vegetative shoot from the previous year, the base of the stem is clothed in leaves of the previous year, in varying states of decay. Those stems are termed phyllopodic or central. This distinction is usually clear in regions with cold winters; it may be blurred in subtropical and tropical areas. In all cases, fertile stems die after fruiting.
In most Carex, the only aboveground stems are those bearing inflorescences. Leaves may be basal or distributed along the stem. Vegetative shoots usually have only basal leaves, with the stemlike aboveground portion being composed only of overlapping leaf sheaths. In a few species, the vegetative shoots are true stems with nodes and internodes. True vegetative stems are characteristic of Carex sect. Ovales, though they are often developed only after fruiting. They are also found in sect. Holarrhenae. In Carex sect. Carex, they are well developed and exceed the fertile stems. In a few species, such as C. assiniboinensis, C. chordorrhiza, C. limosa, and C. mackenziei, some of the vegetative shoots are short, while others differentiate into elongate, leafy stolons that function in vegetative reproduction. In some members of sect. Ovales, the vegetative shoots are very leafy and elongate. In a few species, such as C. tribuloides, C. projecta, C. longii, C. ozarkana, and several others, the vegetative shoots may overwinter and produce new shoots at the nodes; in many species of sect. Ovales, and in sections Carex and Holarrhenae, those stems are strictly annual.
Leaves of Carex are typically linear and have a ligule at the junction of the blade and the sheath. The ligule is mostly fused to the blade, with a narrow, entire or erose-ciliate free portion. Sheaths are often differentiated, with the front (the side opposite the blade) being thin, translucent, and sometimes dotted or veined. When veined, the disintegration and tearing of the sheath front may leave a regular pattern of veins described as ladder-fibrillose. In some wetland species, the sheaths are spongy with large air cavities between the cross veins. Upon drying, the collapse of these air cavities results in the cross veins becoming very prominent, a condition termed septate-nodulose. In some species, such as C. sprengelii, the veins in the sheaths are heavily sclerified and persist as fibrous tufts at the base of the plant and along the rhizome after the leaves decay. These basal fibrous tufts should not be confused with ladder-fibrillose sheaths. Blades are usually V- or M-shaped in cross section. The V-shaped leaves are keeled with a midvein prominent on the abaxial surface and M-shaped leaves have a midvein prominent on the abaxial surface and two mid-lateral veins prominent on the adaxial surface. Both may become essentially flat at maturity. Some species have leaves that are trough-shaped or involute, or even bristlelike. In these, the midvein usually is not keeled and may be no more pronounced than other veins; prominent mid-lateral veins are also lacking. In many species with narrow leaves, the ultimate tip becomes triangular in cross section. Some forest understory species have very broad, flat, short leaves, with short sheaths and may lie essentially flat on the ground.
Inflorescence and flower structures of Carex and other genera in tribe Cariceae (Cymophyllus and Kobresia in the flora, Schoenoxiphium and Uncinia from outside the flora) are difficult to interpret; it is by no means clear whether apparently similar structures in different sections of Carex and in the other genera are homologous (A. A. Reznicek 1990). Staminate flowers consist of three or fewer stamens subtended by a single scale. The arrangement and development of the stamens can be interpreted as each stamen originating from a single flower, the staminate flower therefore being a condensed inflorescence (D. L. Smith and J. S. Faulkner 1976). This interpretation is considered by some authors to be unnecessarily complex and based on inconclusive evidence (T. V. Egorova 1999), so here the staminate flower is regarded as a single flower. The pistillate flower of Carex is believed to be derived by reduction from an inflorescence unit similar to those found in Kobresia and Schoenoxiphium, namely a branch in the axil of a scalelike bract bearing pistillate flower(s) proximally and staminate flowers distally (D. L. Smith and J. S. Faulkner 1976). The first leaf of the axillary branch is modified to a spathelike prophyll. In Schoenoxiphium and Kobresia the prophyll encloses the branch, but the edges are free. In Carex, Cymophyllus, and Uncinia the staminate flowers have been lost and the edges of the prophyll are united to form a perigynium, which has an orifice at the tip through which the style projects. In most species of Carex, the axillary branch (rachilla) is apparently absent, although some minute trace of the rachilla is probably always present (A. A. Reznicek 1990), and in a few species it is well developed and shortly extruded. The flowers are arranged in distinct condensed inflorescences (spikes) that resemble the primary inflorescences (spikelets) of most other genera of Cyperaceae. The spikes are unisexual or bisexual: in bisexual spikes either the distal flowers are staminate and the proximal pistillate (androgynous) or the distal flowers are pistillate and the proximal staminate (gynecandrous).
Inflorescence structure and organization present many problems of interpretation (see summaries by D. L. Smith and J. S. Faulkner 1976; A. A. Reznicek 1990; T. V. Egorova 1999). Inflorescence organization was one of the more important characters used by G. Kükenthal (1909) and others to define subgenera in Carex. Kükenthal divided Carex into four subgenera, which are often referenced in discussions of the classification and evolution of the genus. Subgenus Primocarex consisted of all species in which the inflorescence consisted of a single spike. In different sections of the subgenus, the inflorescence was unisexual, or bisexual and androgynous, or gynecandrous. In subg. Vignea, the spikes were usually bisexual, sessile, and arranged in spikes to elaborately branched panicles. In most sections of subg. Vignea, the styles were bifid and the inflorescence branches lacked prophylls. In subg. Carex (subg. Eucarex), the spikes were most frequently unisexual, the terminal and sometimes some distal lateral spikes being staminate, and the lateral or proximal lateral spikes pistillate; bisexual spikes occurred occasionally. The lateral spikes were peduncled or subsessile and bore a minute, tubular prophyll at the base of the peduncle. The inflorescences were usually spicate or racemose, although more complex inflorescences occurred, especially in Asia. Subgenus Indocarex usually had bisexual spikes that were usually peduncled and usually arranged in branched panicles and had a prophyll that resembled a perigynium at the base of an inflorescence branch. Many deviations from these generalizations exist. For a table summarizing differences among the subgenera as defined by Kükenthal see A. A. Reznicek (1990).
Although the classification and phylogeny of Carex have been the subjects of much debate, the evidence does not allow definitive conclusions. Historic accounts of previously published classifications and phylogenetic interpretations, based primarily on morphologic and anatomic evidence, are available (T. V. Egorova 1999; A. A. Reznicek 1990). The most widely referenced and most recent monograph of the genus is that by G. Kükenthal (1909). His division of the genus into four subgenera has been heavily criticized by many authors, particularly regarding subg. Primocarex. One view maintained that that subg. Primocarex was artificial and that all single-spiked species were derived by reduction from the other three subgenera or even from the genus Uncinia (V. I. Kreczetowicz 1936). Presenting similar criticisms E. Nelmes (1952) distributed sections of subg. Primocarex to other subgenera of Carex and Uncinia, although without making the necessary nomenclatural changes. Despite criticisms Kükenthal’s proposed subdivision of Carex into four subgenera is still widely accepted, albeit with some modifications to meet various criticisms of subg. Primocarex (A. O. Chater 1980; T. V. Egorova 1999). In addition to not accepting subg. Primocarex, T. Koyama (1961b, 1962) did not accept subg. Indocarex and distributed the sections of the subgenus to various parts of subg. Carex. One or two additional subgenera have been proposed as segregates of subg. Carex (e.g., T. V. Egorova 1999); these have not gained general acceptance, and DNA sequence investigations (e.g., E. H. Roalson et al. 2001) do not support their recognition.
In North America, most authors have followed K. K. Mackenzie’s (1931–1935) arrangement of the genus, in which he did not recognize subgenera and instead divided the North American Carex into 71 sections. The sections were narrowly defined, for the most part consisting of groups of species that were very similar morphologically. Mackenzie appears to have arranged sections using much the same criteria although he never explained his arrangement. He started with a group of sections that consisted of single-spiked species, included in G. Kükenthal’s subg. Primocarex, and referred to these sections as “primitive” in his synopsis of the genus. Many single-spiked species, however, were associated with sections Kükenthal had included in the other subgenera. Mackenzie next placed a group of sections together that Kükenthal had included in subg. Vignea, and then a group of sections included by Kükenthal in subgenera Primocarex, Indocarex, and Carex. Thus Mackenzie’s arrangement met many of the criticisms of Kükenthal’s arrangement, but it cannot be applied to the genus on a worldwide basis because few species of subg. Indocarex occur in North America.
The arrangement of the genus followed below is a modified version of K. K. Mackenzie’s system; the sections largely follow his delimitations, except as noted under particular sections. The sections are arranged roughly in a sequence that groups together first those sections usually included in subg. Vignea, including a few species and sections placed by G. Kükenthal in subg. Primocarex (sects. a–q); then sections usually included in subg. Carex, plus sections from subg. Primocarex that are probably related to them (sects. r–jjj); then a group of unispicate sections included by Kükenthal in subg. Primocarex (sects. kkk–qqq); and finally the only North American section included by Kükenthal in subg. Indocarex (sect. rrr). Subgenera are not recognized; although it is possible to assign the multi-spiked sections to subgenera, relationships of a number of unispicate sections are very unclear.
Recent investigations of the genus and related genera utilizing DNA sequences have both clarified and confused the classification and phylogeny of the genus (J. R. Starr et al. 1999; A. C. Yen and R. G. Olmstead 2000, 2000b; E. H. Roalson et al. 2001). All investigations have confirmed the monophylly of subg. Vignea as modified by most recent authors. Subgenus Carex is also generally monophyletic, except that the few species of subg. Indocarex that have been investigated are ambiguously grouped with the bulk of subg. Carex, as are a few species of subg. Primocarex. The bulk of subg. Primocarex, together with Cymophyllus, Uncinia, and Kobresia plus a few species of subg. Carex, form another monophyletic group, with Schoenoxiphium as a sister group. The investigations differ in their placement of subg. Vignea; some place it as a sister group to subg. Carex, while others place it as a sister group to the whole of the tribe Cariceae. Sectional groupings have not been thoroughly investigated, with a few exceptions, and, to date, these investigations have not clarified sectional relationships within the genus. The investigations generally do not support the morphologically based hypothesis (V. I. Kreczetowicz 1936) that most single-spiked species of Carex are recently derived from multi-spiked species, but they have confirmed that a small number of unispicate species are closely related to multi-spiked species.
Numerous interspecific hybrids have been reported in Carex, though few have been produced experimentally. Most hybrids involve species in the same section; some intersectional hybrids are known. Most hybrids are sterile or have very low fertility and most are rare or uncommon. In a few sections, hybrids are much more frequent and may be locally common, in particular in sects. Ceratocystis, Phacocystis, and Vesicariae, where hybrids may be partially fertile. An extensive review of interspecific hybridization involving North American species of Carex was published by (J. Cayouette and P. M. Catling 1992), who accepted reports of 253 hybrids in North America and an additional 73 between species that occur in North America, although to date, hybrids have been found only in Eurasia.
Considering the size and widespread occurrence of Carex, the rather limited economic utility of the genus is surprising. Species of Carex are important constituents of many peat deposits that are exploited commercially. Species of Carex are often important components of moist to wet habitats used as forage for livestock and for herbivorous wildlife. Montane grasslands may also have significant biomass in species of Carex utilized by domestic animals and wildlife. Many species of Carex occurring in eastern Canada, especially the long-rhizomatous ones, are of high forage value (P. M. Catling et al. 1994). Their results are probably of general application as a wide diversity of Carex sections were included. In recent years, species of Carex have greatly increased in popularity in North America as ornamentals. A variety of Eurasian, as well as a few native species, are available commercially. Some of these species have recently become locally naturalized (e.g., Carex pendula); the frequency of naturalization is likely to increase.
For additional information about Carex, see P. M. Catling et al. (1990) and J. M. Bernard and L. Soukupová (1988).
Treatments of Carex do not strictly follow the usual sequence of characteristics; the sequence reflects their complex morphology and the fact that descriptions generally refer to the stage when fruit is developed but not fully ripe.
Selected References
None.
Lower Taxa
Keys
Key to sections of Carex
| 1 | Spike 1 per culm, all flowers attached to main stem in terminal spike. | Key A |
| 1 | Spikes 2+ per culm, some flowers in lateral spikes. | > 2 |
| 2 | All flowers staminate. | Key B |
| 2 | At least some flowers pistillate. | > 3 |
| 3 | Stigmas 2; achenes flat to biconvex in cross section. | Key C |
| 3 | Stigmas (2–)3(–4); achenes ± trigonous, rarely terete, in cross section. | > 4 |
| 4 | Body of perigynium pubsescent, scabrous, hispid, or sometimes papillose, papillae longer than wide | Key D |
| 4 | Body of perigynium glabrous or papillose, papillae mostly not longer than wide. | > 5 |
| 5 | Bracts sheathless or with sheath less than 4 mm, rarely longer, then sheath shorter than diameter of stem. | Key E |
| 5 | Bracts, at least the proximal, with sheath 4+ mm, longer than diameter of stem. | Key F |
Key A. Spike 1 per culm, all flowers attached to main stem in terminal spike.
| 1 | Spike entirely staminate. | > 2 |
| 1 | Spikes with at least some pistillate flowers. | > 8 |
| 2 | Culms distinctly red or purple at base. | > 3 |
| 2 | Culms yellow to brown or black, without red or purple at base. | > 5 |
| 3 | Culms with distal leaves bladeless. | Carex sect. Pictae |
| 3 | Culms with distal leaves with well-developed blades. | > 4 |
| 4 | Fronts of leaf sheaths puberulent; scales ciliate. | Carex sect. Scirpinae |
| 4 | Fronts of leaf sheaths glabrous; scales not ciliate. | Carex sect. Racemosae |
| 5 | Plants densely cespitose; culms serrulate on angles distally. | > 6 |
| 5 | Plants loosely cespitose or not; culms smooth distally. | > 7 |
| 6 | Culms shorter than leaves; widest leaf blades at least 2 mm wide. | Carex sect. Phyllostachyae |
| 6 | Culms clearly exceeding leaves; widest leaf blades less than 2 mm wide. | Carex sect. Stellulatae |
| 7 | Rhizomes stout, dark brown; leaf blades 0.25–4 mm wide. | Carex sect. Dornera |
| 7 | Rhizomes slender, yellow-brown; leaf blades not more than 1 mm wide. | Carex sect. Physoglochin |
| 8 | Stigmas 2; achenes biconvex or flat. | > 9 |
| 8 | Stigmas 3; achenes trigonous. | > 17 |
| 9 | Perigynia 3–4+ times as long as wide, 3–6 mm. | Carex sect. Circinatae |
| 9 | Perigynia 1.2–2(–2.5) times as long as wide, 1.5–4(–4.5) mm. | > 10 |
| 10 | Margins of perigynium beak and often sides of body distinctly and often densely serrulate. | > 11 |
| 10 | Margins of perigynium beak entire or minutely and sparsely serrulate. | > 13 |
| 11 | Perigynia erect or ascending; culms with conspicuous long-persistent basal sheaths. | Carex sect. Nardinae |
| 11 | Perigynia spreading to reflexed when mature; culms with basal sheaths usually not persisting for more than a year. | > 12 |
| 12 | Plants usually not cespitose, single-stemmed; margins and beak of perigyium only weakly and sparsely serrulate. | Carex sect. Physoglochin |
| 12 | Plants cespitose; margins and beak of perigyium coarsely and densely serrulate. | Carex sect. Stellulatae |
| 13 | Spikes gynecandrous; beak of perigyium 0.1–0.3 mm. | Carex sect. Glareosae |
| 13 | Spikes androgynous or pistillate; beak of perigyium 0.3–1 mm. | > 14 |
| 14 | Pistillate scales cuspidate, acute, or acuminate; plants not cespitose. | > 15 |
| 14 | Pistillate scales obtuse; plants cespitose. | > 16 |
| 15 | Perigynia spreading or reflexed at maturity; leaf blades glabrous, less than 1 mm wide. | Carex sect. Physoglochin |
| 15 | Perigynia ascending at maturity; leaf blades somewhat scabrid, widest more than 1 mm wide. | Carex sect. Chordorrhizae |
| 16 | Perigynia few-veined abaxially, not glossy; culms with some red at base. | Carex sect. Capituligerae |
| 16 | Perigynia veinless, somewhat glossy when mature; culms without red at base. | Carex sect. Dornera |
| 17 | Perigynia pubescent or puberulent at least at base of beak, if present. | > 18 |
| 17 | Perigynia glabrous, sometimes minutely papillose. | > 20 |
| 18 | Culms without red or purple at base; single spike androgynous. | Carex sect. Filifoliae |
| 18 | Culms distinctly red or purple at base; spikes usually pistillate. | > 19 |
| 19 | Perigynia with 2 marginal veins, otherwise veinless; beak 0.1–0.5 mm. | Carex sect. Scirpinae |
| 19 | Perigynia with numerous distinct veins; beak absent or rarely to 0.2–0.5 mm. | Carex sect. Pictae |
| 20 | Spikes gynecandrous; beak of perigyium with apical teeth 0.3 mm or longer. | Carex sect. Squarrosae |
| 20 | Spikes androgynous or entirely pistillate; beak of perigyium with apex entire, emarginate, or with teeth less than 0.2 mm. | > 21 |
| 21 | Proximal pistillate scales 10+ mm. | Carex sect. Phyllostachyae |
| 21 | Proximal pistillate scales less than 10 mm. | > 22 |
| 22 | Beak of perigynium mostly 2 mm or longer and at least as long as body. | Carex sect. Phyllostachyae |
| 22 | Beak of perigyium less than 2 mm, or if more, then tapering to body and shorter than body. | > 23 |
| 23 | Perigynia 4–6+ times as long as wide. | > 24 |
| 23 | Perigynia 1.5–4 times as long as wide. | > 25 |
| 24 | Perigynia reflexed at maturity; pistillate scales soon deciduous, the proximal obtuse, shorter than perigynium. | Carex sect. Leucoglochin |
| 24 | Perigynia ascending; pistillate scales persistent, the proximal acute to cuspidate, exceeding perigynium. | Carex sect. Circinatae |
| 25 | Perigynia papillose (15X). | Carex sect. Racemosae |
| 25 | Perigynia smooth, sometimes with minute teeth on margins. | > 26 |
| 26 | Culms with red or purple at base. | > 27 |
| 26 | Culms yellow, brown, or black at base, without red or purple. | > 28 |
| 27 | Perigynia brown or reddish black; fronts of sheaths of culm leaves with red or purple dots. | Carex sect. Obtusatae |
| 27 | Perigynia pale yellow brown with dark tip; fronts of sheaths of culm leaves without red dots. | Carex sect. Rupestres |
| 28 | Perigynia with veins on faces, ± distinct at least over achene. | > 29 |
| 28 | Perigynia with 2 marginal veins, otherwise veinless, or very faint proximal veins. | > 31 |
| 29 | Perigynia rounded at apex, beakless. | Carex sect. Leptocephalae |
| 29 | Perigynia tapering to apex, beaked. | > 30 |
| 30 | Perigynia 3–4 mm, 1.5–2.5 times as long as wide; proximal pistillate scales obtuse to subacute. | Carex sect. Nardinae |
| 30 | Perigynia 4–10 mm, 3–4+ times as long as wide; proximal pistillate scales cuspidate to awned. | Carex sect. Circinatae |
| 31 | Perigynia 3–5 mm, proximal somewhat reflexed at maturity; pistillate scales deciduous before perigynia. | Carex sect. Dornera |
| 31 | Perigynia (4–)4.5–10 mm, ascending to spreading; pistillate scales persistent. | > 32 |
| 32 | Spikes dense, with 15+ perigynia; perigynia inflated, glabrous, glossy, usually not more than 2 times as long as wide. | Carex sect. Inflatae |
| 32 | Spikes lax, at least proximally, with not more than 15 perigynia; perigynia not inflated, not glossy, usually 2–4 times as long as wide. | > 33 |
| 33 | Perigynia oblong-obovoid, 2–3 times as long as wide; achenes 4–5 mm. | Carex sect. Firmiculmes |
| 33 | Perigynia linear-lanceoloid, 3–4 times as long as wide; achenes 1.5–2.5 mm. | Carex sect. Circinatae |
Key B. Spikes 2+ per culm; all flowers staminate
| 1 | Bases of culms and young basal sheaths red or purple tinged (sometimes hidden by old sheaths). | > 2 |
| 1 | Bases of culms and basal sheaths brown or black, without trace of red or purple. | > 4 |
| 2 | Leaf and bract sheaths and sometimes blades puberulent. | Carex sect. Scirpinae |
| 2 | Leaf and bract sheaths and blades glabrous, sometimes finely papillose. | > 3 |
| 3 | Mouth of leaf sheath ciliate; culms, inflorescence axes, and abaxial surface of bracts glabrous. | Carex sect. Acrocystis |
| 3 | Mouth of leaf sheath entire; culms, inflorescence axes, and abaxial surface of bracts finely papillose. | Carex sect. Racemosae |
| 4 | Plants cespitose. | > 5 |
| 4 | Plants not cespitose, some colony forming. | > 6 |
| 5 | Leaves flat. | Carex sect. Deweyanae |
| 5 | Leaves involute or channeled. | Carex sect. Stellulatae |
| 6 | Widest leaves 4–8 mm wide; inflorescences ± capitate, occasionally with proximal 1–2 spikes separated. | Carex sect. Macrocephalae |
| 6 | Widest leaves less than 4 mm wide; inflorescences ovoid to cylindric. | > 7 |
| 7 | Widest leaves not more than 1 mm wide; rhizomes not more than 1 mm wide, mostly without persistent scales; scales at base of culms and on rhizomes not or scarcely fibrous. | Carex sect. Physoglochin |
| 7 | Widest leaves 1+ mm wide; rhizomes mostly more than (0.8–)1 mm wide, covered with persistent scales; scales at base of culms and on rhizomes disintegrating into coarse persistent fibers. | > 8 |
| 8 | Rhizomes with thin, loose cortex, easily detached when dry. | Carex sect. Ammoglochin |
| 8 | Rhizomes with tight cortex, not detaching on drying. | Carex sect. Divisae |
Key C. Spikes 2+ per culm; at least some flowers pistillate; stigmas 2; achenes flat to biconvex in cross section
| 1 | Perigynia pubescent, not papillose. | Carex sect. Acrocystis |
| 1 | Perigynia glabrous, sometimes papillose. | > 2 |
| 2 | Lateral spikes usually pedunculate; proximal bracts sometimes with sheath; peduncles with prophyll at base. | > 3 |
| 2 | Lateral spikes sessile; bracts sheathless; peduncles without or, rarely, with prophyll. | > 9 |
| 3 | Pistillate scales, at least the proximal, long-awned. | Carex sect. Phacocystis |
| 3 | Pistillate scales obtuse to acuminate or cuspidate. | > 4 |
| 4 | Proximal bracts with distinct sheath. | Carex sect. Bicolores |
| 4 | Bracts sheathless or with very short sheath. | > 5 |
| 5 | Perigynia smooth; style persistent on achene. | Carex sect. Vesicariae |
| 5 | Perigynia often papillose over most of surface; style deciduous. | > 6 |
| 6 | Terminal spike gynecandrous, pistillate flowers as many as or more numerous than staminate; lateral spikes short, not much longer than wide. | Carex sect. Bicolores |
| 6 | Terminal spike usually staminate or, sometimes, gynecandrous, staminate flowers then more numerous than pistillate; lateral spikes oblong, distinctly longer than wide. | > 7 |
| 7 | Apex of perigynium beak entire, emarginate, or very shallowly bidentate. | Carex sect. Phacocystis |
| 7 | Apex of perigynium beak distinctly bidentate. | > 8 |
| 8 | Terminal spike usually staminate; stigmas always 2. | Carex sect. Phacocystis |
| 8 | Terminal spike gynecandrous with few perigynia; stigmas 3. | Carex sect. Racemosae |
| 9 | Perigynia papillose (20X); peduncles with or without prophyll. | > 10 |
| 9 | Perigynia smooth; peduncles without prophyll. | > 12 |
| 10 | Terminal spike staminate, androgynous, or if gynecandrous, staminate flowers more numerous than pistillate; lateral spikes at least 2 times as long as wide. | Carex sect. Phacocystis |
| 10 | Terminal spike staminate or gynecandrous, pistillate flowers then as many as or more numerous than staminate; lateral spikes not much longer than wide. | > 11 |
| 11 | Rachis of spikes papillose; peduncles with prophyll. | Carex sect. Bicolores |
| 11 | Rachis of spikes smooth; peduncles without prophyll. | Carex sect. Glareosae |
| 12 | Terminal spike gynecandrous; lateral spikes gynecandrous or pistillate. | > 13 |
| 12 | Terminal spike androgynous, rarely entirely staminate, or entirely pistillate; lateral spikes androgynous, staminate, or pistillate. | > 20 |
| 13 | Margins of perigynia flat, at least in distal 1/2, flat portion (0.1–)0.2 mm wide or wider at tip of achene and base of beak. | > 14 |
| 13 | Margins of perigynia rounded or with flat portion not more than 0.1 mm wide. | > 16 |
| 14 | Achenes rounded at apex, style dehiscing at surface of achene; style conspicuously enlarged at base. | Carex sect. Deweyanae |
| 14 | Achenes with short apiculus formed by persistent base of style; style not conspicuously enlarged at base. | > 15 |
| 15 | Longest bract 5–20(–25) cm, at least (3–)5 times as long as inflorescence. | Carex sect. Cyperoideae |
| 15 | Proximal bract not more than 5 cm, not more than 2 times as long as inflorescence. | Carex sect. Ovales |
| 16 | Margins of perigynia rounded or with very narrow rounded edge; achenes nearly filling perigynium bodies. | Carex sect. Glareosae |
| 16 | Margins of perigynia sharply edged or narrowly winged; achenes distinctly smaller than bodies. | > 17 |
| 17 | Inflorescences in fruit 1–1.5 times as long as wide. | Carex sect. Ovales |
| 17 | Inflorescences in fruit (1.5–)2+ times as long as wide. | > 18 |
| 18 | At least proximal perigynia in each spike spreading. | Carex sect. Stellulatae |
| 18 | All perigynia erect or ascending. | > 19 |
| 19 | Perigynia with margins of body and beak entire. | Carex sect. Ovales |
| 19 | Perigynia with distal margins of body and usually base of beak serrulate, sometimes sparsely. | Carex sect. Deweyanae |
| 20 | Sheath fronts of proximal cauline leaves transversely rugose. | > 21 |
| 20 | Sheath fronts of proximal cauline leaves smooth or very weakly transversely rugose. | > 23 |
| 21 | Perigynia mostly more than 2 times as long as wide, widest near base. | Carex sect. Vulpinae |
| 21 | Perigynia mostly not more than 2 times as long as wide, widest near middle. | > 22 |
| 22 | Inflorescences usually branched, at least proximally, usually with more than 15 spikes; pistillate scales usually yellow or brown, sometimes with hyaline margins, 3-veined. | Carex sect. Multiflorae |
| 22 | Inflorescences unbranched or with 1–2 short branches proximally, with not more than 15 spikes; pistillate scales greenish hyaline, 1-veined. | Carex sect. Phaestoglochin |
| 23 | Fronts of leaf sheaths dotted red, brown, or yellow. | > 24 |
| 23 | Fronts of leaf sheaths not dotted red, brown, or yellow. | > 26 |
| 24 | Perigynia widest near base; culms usually more than 1 mm wide. | Carex sect. Vulpinae |
| 24 | Perigynia widest near middle; culms usually not more than 1 mm wide distally. | > 25 |
| 25 | Plants densely cespitose, short-rhizomatous; pistillate scales acute to acuminate. | Carex sect. Heleoglochin |
| 25 | Plants loosely cespitose, sometimes long-rhizomatous; pistillate scales, at least distally, obtuse. | Carex sect. Multiflorae |
| 26 | Perigynium beak not more than 0.25 mm, margins entire, not serrulate. | Carex sect. Dispermae |
| 26 | Perigynium beak more than 0.25 mm, margins often serrulate. | > 27 |
| 27 | Distal leaves of culms with front of sheaths green-veined, not differentiated from rest of sheath. | Carex sect. Holarrhenae |
| 27 | Distal leaves of culms with front of sheaths with at least narrow hyaline or whitish hyaline band extending at least 1/2 length of sheath. | > 28 |
| 28 | Perigynia with flat, winglike margins 0.1 mm wide or wider distally; plants long-rhizomatous, not cespitose, sometimes colonial. | Carex sect. Ammoglochin |
| 28 | Perigynia without or with flat margins less than 0.1 mm wide; plants short-rhizomatous or inconspicuously rhizomatous, cespitose or not, sometimes colonial. | > 29 |
| 29 | Plants cespitose. | > 30 |
| 29 | Plants cespitose or colonial from creeping rhizomes. | > 32 |
| 30 | Spikes not consistently androgynous, terminal either entirely staminate or pistillate, lateral spikes irregularly pistillate or staminate or mixed. | Carex sect. Stellulatae |
| 30 | Spikes ± consistently androgynous, occasionally some lateral spikes entirely pistillate. | > 31 |
| 31 | Perigynium widest near base, tapering from base to beak. | Carex sect. Vulpinae |
| 31 | Perigynium widest above base, often abruptly beaked. | Carex sect. Phaestoglochin |
| 32 | Inflorescences globose or ovoid-globose, very dense so that individual spikes are indistinguishable; spikes consistently androgynous. | Carex sect. Foetidae |
| 32 | Inflorescences ovoid to oblong, usually moderately dense, at least proximal spikes distinguishable; rarely inflorescence ovoid-globose, then spikes mostly pistillate. | > 33 |
| 33 | Culms scabrous or serrulate on angles distally. | Carex sect. Divisae |
| 33 | Culms smooth on angles distally. | > 34 |
| 34 | Perigynia strongly veined on both faces; beak not more than 0.6 mm, less than 1/5 length of body. | Carex sect. Chordorrhizae |
| 34 | Perigynia veinless or weakly veined adaxially; beak 0.2+ mm, at least 1/4 length of body. | Carex sect. Divisae |
Key D. Spikes 2+ per culm; at least some flowers pistillate; stigmas (2–)3(–4); achenes usually trigonous in cross section; body of perigynium pubescent to hispid, sometimes papillose, papillae longer than wide
| 1 | Pistillate spikes all basal. | Carex sect. Acrocystis |
| 1 | Pistillate spikes, at least some, on an elongate stem. | > 2 |
| 2 | Bracts of proximal nonbasal spike with well-developed sheath at least 4 mm. | > 3 |
| 2 | Bract of proximal nonbasal spike sheathless or with sheath less than 4 mm. | > 13 |
| 3 | Beak of perigynium with distinct teeth usually at least 0.6 mm. | Carex sect. Carex |
| 3 | Beak of perigynium entire, notched, or with teeth less than 0.6 mm. | > 4 |
| 4 | Bracts of proximal nonbasal spikes bladeless or with blade not more than 2 mm. | > 5 |
| 4 | Bracts of proximal nonbasal spikes with blade at least 3 mm, often much longer. | > 6 |
| 5 | Perigynia 2–3.5 mm; widest leaf blades 2–4 mm wide. | Carex sect. Clandestinae |
| 5 | Perigynia 4–5 mm; widest leaf blades 4+ mm wide. | Carex sect. Pictae |
| 6 | Achenes with persistent enlarged circular base of style at apex. | Carex sect. Mitratae |
| 6 | Achenes with style not conspicuously enlarged at base, usually deciduous or at most leaving short apiculus at apex. | > 7 |
| 7 | Leaves pubescent or pilose. | Carex sect. Hymenochlaenae |
| 7 | Leaves usually glabrous. | > 8 |
| 8 | Pistillate scales dark brown to almost black; proximal leaf blades with marginal veins equally prominent; leaves on culms as wide as basal leaves. | > 9 |
| 8 | Pistillate scales hyaline, green, or pale brown; proximal leaf blades usually with 2 marginal veins more prominent than midvein on adaxial surface; basal leaves often conspicuously wider than leaves on culms. | > 10 |
| 9 | Distal leaves on culms bladeless or with blade less than 1 cm. | Carex sect. Clandestinae |
| 9 | Distal leaves on culms with blade at least 2 cm. | Carex sect. Aulocystis |
| 10 | Bases of plants brown, without trace of red or purple. | > 11 |
| 10 | Bases of plants distinctly red or purple. | > 12 |
| 11 | Perigynia obscurely veined or to 6-veined; proximal bract sheaths to 35 mm. | Carex sect. Triquetrae |
| 11 | Perigynia strongly 12–30-veined; proximal bract sheaths not more than 5 mm. | Carex sect. Hallerianae |
| 12 | Proximal pistillate scales awned; leaves somewhat septate-nodulose; plants usually colonial, long-rhizomatous. | Carex sect. Paludosae |
| 12 | Proximal pistillate scales obtuse to acuminate; leaves not septate-nodulose; plants cespitose, short-rhizomatous. | Carex sect. Hymenochlaenae |
| 13 | Perigynia 10+ mm. | > 14 |
| 13 | Perigynia less than 10 mm. | > 15 |
| 14 | Pistillate spikes globose, about as long as wide; staminate spikes usually 1. | Carex sect. Lupulinae |
| 14 | Pistillate spikes cylindric, much longer than wide; staminate spikes 1–8. | Carex sect. Carex |
| 15 | Tip of perigynium beak with 2 teeth at least 0.6 mm. | Carex sect. Carex |
| 15 | Tip of perigynium beak entire or with 2 teeth less than 0.6 mm. | > 16 |
| 16 | Terminal spike gynecandrous or pistillate. | > 17 |
| 16 | Terminal spike staminate or, rarely, androgynous. | > 18 |
| 17 | Leaf sheaths and usually blades pilose. | Carex sect. Porocystis |
| 17 | Leaf sheaths puberulent and blades usually glabrous. | Carex sect. Scirpinae |
| 18 | Leaf sheaths and usually blades pubescent. | > 19 |
| 18 | Leaf sheaths and blades glabrous. | > 23 |
| 19 | Pistillate scales sometimes pubescent; pistillate spikes with 40–200 perigynia. | Carex sect. Paludosae |
| 19 | Pistillate scales glabrous; pistillate spikes with not more than 40(–50) perigynia. | > 20 |
| 20 | Perigynia usually not more than 3.2 mm, apex rounded and beakless or abruptly beaked. | Carex sect. Porocystis |
| 20 | Perigynia 3.5+ mm, apex tapering or abruptly beaked. | > 21 |
| 21 | Pistillate spikes with longer peduncles 1+ cm; perigynia more than 3 times as long as wide, tapering gradually to base. | Carex sect. Hymenochlaenae |
| 21 | Pistillate spikes subsessile or with peduncles not more than 1 cm; perigynia not more than 3 times as long as wide, abruptly contracted to short stipe at base. | > 22 |
| 22 | Perigynia distinctly 12–30-veined; beak not more than 0.5 mm. | Carex sect. Hallerianae |
| 22 | Perigynia veinless except for 2 marginal veins; beak 0.7–1.5+ mm. | Carex sect. Hirtifoliae |
| 23 | All or most spikes androgynous. | Carex sect. Schiedeanae |
| 23 | Most spikes entirely pistillate or staminate, occasionally with 1 androgynous. | > 24 |
| 24 | Achenes with enlarged persistent circular base of style at apex. | Carex sect. Mitratae |
| 24 | Achenes with style not conspicuously enlarged at base, usually deciduous or at most forming an apiculus at apex. | > 25 |
| 25 | Leaf blades scabrous on adaxial surface; beak of perigyium recurved. | Carex sect. Anomalae |
| 25 | Leaf blades glabrous on adaxial surface, often with rough margins or rough tip; beak of perigyium straight. | > 26 |
| 26 | Fronts of sheaths of proximal leaves ladder-fibrillose; leaves and sheaths septate-nodulose, sometimes obscurely. | Carex sect. Paludosae |
| 26 | Fronts of leaf sheaths not ladder-fibrillose, sometimes breaking into longitudinal fibers; leaves and sheaths not septate-nodulose. | > 27 |
| 27 | Perigynia strongly 12–30-veined. | > 28 |
| 27 | Perigynia 0–12-veined. | > 30 |
| 28 | Leaf blades papillose; pistillate scales 3–7(10)-veined. | Carex sect. Hallerianae |
| 28 | Leaf blades not papillose; pistillate scales 1–3-veined. | > 29 |
| 29 | Leaf blades, at least distally, M-shaped in cross section when young, adaxial surface usually with 2 marginal veins more prominent than midvein; staminate spikes 1–4. | Carex sect. Paludosae |
| 29 | Leaf blades V-shaped in cross section when young, adaxial surface without 2 marginal veins more prominent than midvein; staminate spike 1. | Carex sect. Acrocystis |
| 30 | Perigynia papillose; pistillate spikes cylindric with usually more than 30 perigynia. | Carex sect. Thuringiaca |
| 30 | Perigynia pubescent; pistillate spikes ovoid with not more than 25 perigynia. | > 31 |
| 31 | Plants with at least some pistillate spikes basal; culms usually much shorter than leaves. | Carex sect. Acrocystis |
| 31 | Plants with most pistillate spikes on obvious elongated stems; culms shorter or longer than leaves. | > 32 |
| 32 | Distal leaves (often near base) bladeless or blades not more than 1 cm and not longer than sheaths. | Carex sect. Clandestinae |
| 32 | Distal leaves with blades more than 2 cm, longer than sheaths. | Carex sect. Acrocystis |
Key E. Spikes 2+ per culm, at least some flowers pistillate; stigmas (2–)3(–4); achenes usually ± trigonous in cross section; body of perigynium glabrous or papillose, papillae then mostly not longer than wide; bracts sheathless or sheath less than 4 mm, rarely longer, then sheath shorter than diameter of stem
| 1 | Tip of perigynium beak with 2 teeth at least (0.4–)0.5 mm. | > 2 |
| 1 | Tip of perigynium beak entire, emarginate, or with 2 teeth less than 0.5 mm. | > 18 |
| 2 | Perigynia with 2 distinct marginal veins, otherwise veinless or only very faintly veined; leaves not septate-nodulose. | Carex sect. Hymenochlaenae |
| 2 | Perigynia with 5+ distinct veins; at least proximal leaves septate-nodulose, rarely not. | > 3 |
| 3 | Perigynia with serrulate wing on margins; spikes usually 20+, sessile, pistillate or androgynous and similar in appearance, forming a dense, ovoid or oblong head, rarely with proximal spike separated. | Carex sect. Macrocephalae |
| 3 | Perigynia without wing on margins; spikes not more than 10, usually at least proximal shortly pedunculate, sometimes subsessile, distal and proximal spikes usually dissimilar in appearance, usually not crowded into dense head. | > 4 |
| 4 | Pistillate scales obtuse to acuminate, awnless or at most with a rough apiculus. | > 5 |
| 4 | Pistillate scales, at least some, with scabrous awn. | > 8 |
| 5 | Staminate spike usually 1; perigynia 15–20-veined, 10–20 mm. | Carex sect. Lupulinae |
| 5 | Staminate spikes usually 1–3+; perigynia 6–15(–22)-veined, 4–10(–12.5) mm. | > 6 |
| 6 | Perigynia 6–14(–15)-veined. | Carex sect. Vesicariae |
| 6 | Perigynia 14–25-veined. | > 7 |
| 7 | Perigynia narrowly ovate to subglobose, 2–2.5 times as long as wide. | Carex sect. Paludosae |
| 7 | Perigynia elliptic to ovate, 3–4.5 times as long as wide. | Carex sect. Vesicariae |
| 8 | Perigynia (9–)10+ mm. | > 9 |
| 8 | Perigynia not more than 9 mm. | > 10 |
| 9 | Pistillate spikes globose,ovoid, or cylindric, about as long as wide; staminate spikes usually 1. | Carex sect. Lupulinae |
| 9 | Pistillate spikes cylindric, much longer than wide; staminate spikes (1–)2–6. | Carex sect. Carex |
| 10 | Distal pistillate scales with awn at least 1/2 as long as body. | Carex sect. Vesicariae |
| 10 | Distal pistillate scales acute to short-awned, awn less than 1/2 as long as body. | > 11 |
| 11 | Beak of perigynia with teeth 1.1–3 mm. | Carex sect. Carex |
| 11 | Beak of perigynia with teeth often not more than 1 mm. | > 12 |
| 12 | Staminate spikes 1(–4); perigynium beak more than 1.7 mm. | Carex sect. Paludosae |
| 12 | Staminate spikes 1–6; perigynium beak often less than 1.7 mm. | > 13 |
| 13 | Perigynia veined only at base; widest leaves not more than 4 mm wide. | Carex sect. Paludosae |
| 13 | Perigynium veined to tip of body and often into beak; widest leaves mostly more than 4 mm wide. | > 14 |
| 14 | Pistillate scales with margins serrulate distally; awn, when present, rough. | > 15 |
| 14 | Pistillate scales with margins entire; awn, when present, usually smooth. | > 16 |
| 15 | Perigynia 3.1–4.8 × 0.9–1.5(–1.8) mm; staminate spikes 1–2. | Carex sect. Vesicariae |
| 15 | Perigynia 2.5–8 × 1.2–3.5 mm; staminate spikes usually 3–7. | Carex sect. Paludosae |
| 16 | Perigynia 9–15-veined. | Carex sect. Vesicariae |
| 16 | Perigynia 14–25-veined. | > 17 |
| 17 | Perigynia narrowly ovate to subglobose, 2– 2.5 times as long as wide. | Carex sect. Paludosae |
| 17 | Perigynia elliptic to ovate, 3–4.5 times as long as wide. | Carex sect. Vesicariae |
| 18 | Perigynia minutely papillose, at least distally (20X). | > 19 |
| 18 | Perigynia not papillose, essentially smooth. | > 24 |
| 19 | Some roots with yellow-brown felty covering. | Carex sect. Limosae |
| 19 | Roots brown or black, without yellow-brown felty covering, rarely with white felty covering. | > 20 |
| 20 | Leaf blades and/or sheaths pubescent, at least at junction of blade and sheath. | Carex sect. Porocystis |
| 20 | Leaf blades and sheaths glabrous. | > 21 |
| 21 | Terminal spike gynecandrous. | Carex sect. Racemosae |
| 21 | Terminal spike staminate or androgynous. | > 22 |
| 22 | Proximal pistillate scales with awn 1.2–3.5 mm; staminate scales awned. | Carex sect. Glaucescentes |
| 22 | Pistillate scales obtuse to acuminate or with awn less than 1 mm; staminate scales not awned. | > 23 |
| 23 | Achenes smaller than to almost filling bodies of perigynia. | Carex sect. Racemosae |
| 23 | Achenes, at most, filling only proximal 1/2 of bodies of perigynia. | Carex sect. Scitae |
| 24 | Terminal spike gynecandrous. | > 25 |
| 24 | Terminal spike staminate or androgynous. | > 31 |
| 25 | Perigynia with distinct beak 0.5–4 mm. | > 26 |
| 25 | Perigynia beakless or with beak not more than 0.5 mm. | > 27 |
| 26 | Larger spikes usually with more than 50 perigynia; achenes 2–3 mm. | Carex sect. Squarrosae |
| 26 | Larger spikes with not more than 40 perigynia; achenes 1–2 mm. | Carex sect. Ceratocystis |
| 27 | Adaxial side of leaves with 2 marginal veins more prominent than midvein; young leaves M-shaped in cross section. | > 28 |
| 27 | Adaxial side of leaves without 2 marginal veins more prominent than midvein; young leaves V-shaped or rounded in cross section. | > 29 |
| 28 | Perigynia subcircular, not more than 1.2 times as long as wide; apex rounded, abruptly beaked; sheaths of proximal leaves septate-nodulose. | Carex sect. Shortianae |
| 28 | Perigynia ovoid, usually at least 1.5 times as long as wide; apex tapered to beak; sheaths of proximal leaves not septate-nodulose. | Carex sect. Hymenochlaenae |
| 29 | Leaf blades and/or sheaths pubescent, at least at junction of blade and sheath. | Carex sect. Porocystis |
| 29 | Leaf blades and sheaths glabrous. | > 30 |
| 30 | Perigynia erect or ascending. | Carex sect. Racemosae |
| 30 | Perigynia ascending, spreading at about right angles, or reflexed when mature. | Carex sect. Ceratocystis |
| 31 | Leaves and/or sheaths pubescent, at least at junction of blade and sheath. | > 32 |
| 31 | Leaves and sheaths usually glabrous, rarely papillose. | > 35 |
| 32 | Larger leaves 8–23 mm wide, only sheaths pubescent. | Carex sect. Anomalae |
| 32 | Leaves not more than 8 mm wide, blades and usually sheaths pubescent. | > 33 |
| 33 | Perigynium beak 0.5–3 mm, often 1+ mm, about 1/2 length of body; proximal pistillate scales awned. | Carex sect. Hymenochlaenae |
| 33 | Perigynium beak absent or not more than 0.5(–0.7) mm, not more than 1/4 length of body; proximal pistillate scales acute, acuminate or cuspidate. 1. | > 34 |
| 34 | Perigynia 3.7–5.5 mm; culms ± smooth distally. | Carex sect. Longicaules |
| 34 | Perigynia 1.7–4 mm; culms rough distally. | Carex sect. Porocystis |
| 35 | Style persistent on achene in fruit; larger leaves and sheaths usually at least sparsely septate-nodulose, rarely not. | > 36 |
| 35 | Style deciduous; larger leaves and sheaths sometimes septate-nodulose, more often not. | > 41 |
| 36 | Larger leaves and sheaths not septate-nodulose; perigynia obscurely veined on faces. | Carex sect. Hispidae |
| 36 | Larger leaves and sheaths distinctly septate-nodulose; perigynia usually strongly veined on faces. | > 37 |
| 37 | Perigynia (9–)10+ mm; staminate spike usually 1. | Carex sect. Lupulinae |
| 37 | Perigynia not more than 10 mm; staminate spikes 1–5(–7). | > 38 |
| 38 | Pistillate scales with margins serrulate distally, apex usually rough-awned. | > 39 |
| 38 | Pistillate scales with margins entire, apex awnless or with short, smooth awn. | > 40 |
| 39 | Distal pistillate scales with apex long-awned, awn at least 1/2 as long as body. | Carex sect. Vesicariae |
| 39 | Distal pistillate scales with apex acute to short-awned, awn less than 1/2 as long as body. | Carex sect. Paludosae |
| 40 | Perigynia slightly to strongly inflated, thin walled, yellowish to purlish, shiny. | Carex sect. Vesicariae |
| 40 | Perigynia not inflated, thick walled, brownish, dull. | Carex sect. Paludosae |
| 41 | Leaf blades, at least widest, M-shaped in cross section when young, adaxial surface with 2 marginal veins more prominent than midvein. | > 42 |
| 41 | Leaf blades V-shaped in cross section when young, adaxial surface without 2 marginal veins more prominent than midvein. | > 44 |
| 42 | Widest leaf blades 8–23 mm wide, septate-nodulose. | Carex sect. Anomalae |
| 42 | Widest leaf blades not more than 6 mm wide, not septate-nodulose. | > 43 |
| 43 | Pistillate scales awned, longest awn 0.5+ mm. | Carex sect. Griseae |
| 43 | Pistillate scales obtuse to acuminate or short-awned, awn not more than 0.2 mm. | Carex sect. Hymenochlaenae |
| 44 | Proximal perigynia in each spike spreading at right angles or reflexed at ma-turity; leaf blades and sheaths sparsely septate-nodulose. | Carex sect. Ceratocystis |
| 44 | Proximal perigynia in each spike ascending or spreading-ascending; leaf blades and sheaths not septate-nodulose. | > 45 |
| 45 | Plant base brown or blackish, without trace of red or purple. | > 46 |
| 45 | Plant base red or purple tinged, sometimes sparsely. | > 47 |
| 46 | Longest pistillate scales 10+ mm, green, often leaflike; lateral spikes basal. | Carex sect. Phyllostachyae |
| 46 | Longest pistillate scales less than 5 mm, black or dark brown, not leaf like; at least some lateral spikes cauline. | Carex sect. Scitae |
| 47 | Perigynia distinctly veined on faces; pistillate scales brown or black. | Carex sect. Racemosae |
| 47 | Perigynia veinless or with veins only proximally; pistillate scales white-hyaline or red-brown. | > 48 |
| 48 | Widest leaves 2–4.5 mm wide; plants usually with several long-peduncled basal pistillate spikes. | Carex sect. Acrocystis |
| 48 | Widest leaf blades 1–2 mm wide; plants without long-peduncled basal pistillate spikes. | Carex sect. Lamprochlaenae |
Key F. Spikes 2+ per culm, at least some flowers pistillate; stigmas (2–)3(–4); achenes usually ± trigonous in cross section; body of perigynium glabrous or papillose, papillae mostly not longer than wide; bracts, at least proximal, with sheath 4+ mm, longer than diameter of stem
| 1 | Apex of perigynium beak terminated by 2 teeth, mostly at least 0.5 mm. | > 2 |
| 1 | Apex of perigynium beak entire, emarginate, or with teeth mostly less than 0.5 mm. | > 17 |
| 2 | Perigynia 4+ times as long as wide (8–15 × 1–3 mm). | > 3 |
| 2 | Perigynia not more than 4 times as long as wide. | > 4 |
| 3 | Apical teeth of perigynium beak reflexed; achenes elongate; pistillate scales with 1-veined center. | Carex sect. Collinsiae |
| 3 | Apical teeth of perigynium beak erect; achenes oblong-obovoid or obovoid; at least proximal pistillate scales with 3–5(–7)-veined center. | Carex sect. Rostrales |
| 4 | Perigynia (9–)10 mm or longer. | > 5 |
| 4 | Perigynia not more than 10 mm. | > 8 |
| 5 | Sheaths, at least proximal sheath fronts, densely tomentose at mouth; apical teeth of perigynium beak often more than 1 mm. | Carex sect. Carex |
| 5 | Sheaths glabrous; apical teeth of perigynium beak not more than 1 mm. | > 6 |
| 6 | Perigynia 7–11-, 5–12-, or 12–25-veined. | Carex sect. Vesicariae |
| 6 | Perigynia 12–34-veined. | > 7 |
| 7 | Basal and proximal leaf sheaths reddish or purplish. | Carex sect. Lupulinae |
| 7 | Basal and proximal leaf sheaths yellowish to brown, without trace of red or purple. | Carex sect. Rostrales |
| 8 | At least proximal pistillate scales with long, rough awn. | > 9 |
| 8 | All pistillate scales obtuse to acuminate or cuspidate. | > 13 |
| 9 | Perigynia with 2 strong marginal veins, otherwise veinless or veined only proximally; leaves not septate-nodulose. | Carex sect. Hymenochlaenae |
| 9 | Perigynia with 5+ strong veins extending length of bodies; leaves septate-nodulose. | > 10 |
| 10 | Perigynium beak with apical teeth (0.4–)0.6–3 mm, often longer than 1 mm. | Carex sect. Carex |
| 10 | Perigynium beak with apical teeth not more than 1 mm. | > 11 |
| 11 | Perigynium body obovoid, widest distally; proximal bract at least 3 times as long as inflorescence. | Carex sect. Squarrosae |
| 11 | Perigynium body ovoid or lanceoloid or ellipsoid, widest at middle or proximally; proximal bract usually not more than 2 times as long as inflorescence. | > 12 |
| 12 | Perigynium beak 0.9–1.7 mm; mature perigynia dull. | Carex sect. Paludosae |
| 12 | Perigynium beak 0.2–6 mm; mature perigynia somewhat glossy. | Carex sect. Vesicariae |
| 13 | Culms with some red or purple at base. | > 14 |
| 13 | Culms brown or black at base, without trace of red or purple. | > 15 |
| 14 | At least proximal perigynia in each spike spreading or reflexed; leaves sparsely septate-nodulose. | Carex sect. Vesicariae |
| 14 | All perigynia erect or ascending; leaves not septate-nodulose. | Carex sect. Hymenochlaenae |
| 15 | Pistillate scales with 5–7-veined center. | Carex sect. Rostrales |
| 15 | Pistillate scales with 1–3-veined center. | > 16 |
| 16 | Leaves not septate-nodulose. | Carex sect. Hymenochlaenae |
| 16 | Leaves at least sparingly septate-nodulose. | Carex sect. Ceratocystis |
| 17 | Leaf blades variously hairy. | > 18 |
| 17 | Leaf blades glabrous. | > 21 |
| 18 | Plant brown or black at base. | > 19 |
| 18 | Plant with at least some red or purple at base. | > 20 |
| 19 | Pistillate scales acute or shortly cuspidate, with midvein protruding from body of scale less than 0.2 mm. | Carex sect. Longicaules |
| 19 | Pistillate scales, at least proximal, with rough awn 0.1–8.3 mm. | Carex sect. Griseae |
| 20 | Sheaths of proximal bracts more than 5 mm. | Carex sect. Hymenochlaenae |
| 20 | Sheaths of proximal bracts not more than 5 mm. | Carex sect. Longicaules |
| 21 | Bracts without blades. | > 22 |
| 21 | Bracts, at least proximal, with distinct blade. | > 23 |
| 22 | Leaves not more than 1 mm wide. | Carex sect. Albae |
| 22 | Leaves much wider, often over 10 mm wide. | Carex sect. Careyanae |
| 23 | Young leaves V-shaped or rounded in cross section, adaxial surface without 2 marginal veins more prominent than midvein or other veins. | > 24 |
| 23 | Leaf blades M-shaped in cross section when young, adaxial surface with 2 marginal veins more prominent than midvein and other marginal veins, sometimes apparent only on proximal leaves and on proximal part of blade. | > 40 |
| 24 | Perigynium beak with 2 distinct terminal teeth, usually more than 0.2 mm. | > 25 |
| 24 | Perigynium beak entire, emarginate, or with 2 apical teeth not exceeding 0.2 mm. | > 31 |
| 25 | At least proximal pistillate scales awned, awn at least 1/2 as long as body; leaves conspicuously septate-nodulose. | > 26 |
| 25 | Pistillate scales obtuse to acuminate, sometimes very shortly awned; leaves not or only weakly septate-nodulose. | > 28 |
| 26 | Base of culm strongly red or purple; leaves 2–4 mm wide. | Carex sect. Vesicariae |
| 26 | Base of culm brown, without or with only trace of red or purple; leaves 4–15 mm wide. | > 27 |
| 27 | Distal pistillate scales with awn at least about as long as body. | Carex sect. Vesicariae |
| 27 | Distal pistillate scales acute, acuminate, or short-awned, awn less than 1/2 length of body. | Carex sect. Paludosae |
| 28 | Perigynia often black, at least distally, or black-mottled (even when immature). | Carex sect. Aulocystis |
| 28 | Perigynia yellow-brown to dark brown when mature, not black-mottled. | > 29 |
| 29 | Plants with long-creeping rhizomes; leaves usually not septate-nodulose. | Carex sect. Paniceae |
| 29 | Plants with short-ascending rhizomes; leaves at least sparingly septate-nodulose. | > 30 |
| 30 | Proximal perigynia in each spike spreading or reflexed. | Carex sect. Ceratocystis |
| 30 | Proximal perigynia in each spike ascending or spreading-ascending. | Carex sect. Spirostachyae |
| 31 | Perigynia often black at least distally, or black-mottled (even when immature). | Carex sect. Aulocystis |
| 31 | Perigynia yellow-brown to dark brown when mature, not mottled black. | > 32 |
| 32 | Fronts of leaf sheaths ladder-fibrillose; staminate spikes usually 2–4. | Carex sect. Hispidae |
| 32 | Fronts of leaf sheaths not ladder-fibrillose; staminate spikes solitary, rarely with second much smaller spike. | > 33 |
| 33 | Perigynia rounded at base, sides proximally distinctly convex. | > 34 |
| 33 | Perigynia tapering at base, sides straight or only slightly convex proximally. | > 35 |
| 34 | Perigynia with veins slightly prominent. | Carex sect. Granulares |
| 34 | Perigynia with veins slightly impressed. | Carex sect. Griseae |
| 35 | Perigynia rounded at apex, beakless or with beak less than 0.3 mm. | > 36 |
| 35 | Perigynia tapering to beak at least (0.3–)0.5 mm. | > 37 |
| 36 | Widest leaf blades usually 5+ mm wide; plants usually cespitose. | Carex sect. Laxiflorae |
| 36 | Widest leaf blades less than 5 mm wide; plants usually not cespitose. | Carex sect. Paniceae |
| 37 | Proximal perigynia in each spike spreading at right angles or reflexed at maturity; leaves and sheaths sparsely septate-nodulose. | Carex sect. Ceratocystis |
| 37 | Proximal perigynia in each spike ascending or spreading-ascending; leaves and sheaths not septate-nodulose. | > 38 |
| 38 | Plants usually colonial; perigynia and leaves often papillose. | Carex sect. Paniceae |
| 38 | Plants cespitose; perigynia and leaves not papillose. | > 39 |
| 39 | Pistillate spikes erect or somewhat spreading, peduncles usually not longer than spikes; perigynia 10–16-veined, usually speckled red-brown. | Carex sect. Spirostachyae |
| 39 | Pistillate spikes spreading or pendent, mostly with peduncles longer than spikes (spikes often erect on short peduncles in arctic and high mountain dwarf plants); perigynia veinless except for 2 marginal veins or with fewer than 10 veins, not speckled red-brown. | Carex sect. Chlorostachyae |
| 40 | Perigynium beakless or with beak 0.5 mm or less, entire or with 2 apical teeth less than 0.1 mm. | > 41 |
| 40 | Perigynium with distinct beak more than 0.5 mm, usually with apical teeth 0.1+ mm. | > 51 |
| 41 | Widest leaf blades (usually basal) 10+ mm wide. | > 42 |
| 41 | Widest leaves not more than 10 mm wide. | > 44 |
| 42 | Culms usually 90+ cm; pistillate spikes (30–)60+ mm, with at least 100 perigynia in each. | Carex sect. Rhynchocystis |
| 42 | Culms not exceeding 60(–80) cm; pistillate spikes not more than 60 mm, with not more than 30 perigynia. | > 43 |
| 43 | Perigynia sharply trigonous in cross section. | Carex sect. Careyanae |
| 43 | Perigynia trigonous with rounded angles in cross section. | Carex sect. Laxiflorae |
| 44 | Perigynia not prominently veined, veins somewhat impressed. | Carex sect. Griseae |
| 44 | Perigynia at least slightly prominently veined or veinless except for 2 marginal veins. | > 45 |
| 45 | Perigynia rounded at base, sides proximally convex. | Carex sect. Granulares |
| 45 | Perigynia tapering at base, sides proximally straight, concave or slightly convex. | > 46 |
| 46 | Perigynia transversely wrinkled; leaf sheaths sparsely septate-nodulose. | Carex sect. Shortianae |
| 46 | Perigynia not transversely wrinkled; leaf sheaths not septate-nodulose. | > 47 |
| 47 | Perigynia sharply trigonous in cross section. | Carex sect. Careyanae |
| 47 | Perigynia terete or with rounded angles in cross section. | > 48 |
| 48 | Perigynia with 2 marginal veins and not more than 10 veins on faces. | > 49 |
| 48 | Perigynia with more than 12 veins. | > 50 |
| 49 | Base of plant red, often very dark. | Carex sect. Hymenochlaenae |
| 49 | Base of plant brown, without trace of red. | Carex sect. Chlorostachyae |
| 50 | Plants usually colonial, not cespitose; perigynia papillose at least faintly. | Carex sect. Paniceae |
| 50 | Plants usually cespitose; perigynia not papillose. | Carex sect. Laxiflorae |
| 51 | Perigynia with 2 distinct marginal veins, otherwise veinless or with very weak veins proximally. | > 52 |
| 51 | Perigynia with more than 2 veins extending most of length of bodies. | > 55 |
| 52 | Perigynium beak entire, emarginate, or with apical teeth not more than 0.1 mm. | > 53 |
| 52 | Perigynium beak with apical teeth 0.2–1 mm. | > 54 |
| 53 | Widest leaves mostly 5+ mm wide. | Carex sect. Laxiflorae |
| 53 | Widest leaves 1–4 mm wide. | Carex sect. Chlorostachyae |
| 54 | Perigynium beak somtimes more than 2 mm. | Carex sect. Hymenochlaenae |
| 54 | Perigynium beak usually not more than 1 mm. | Carex sect. Paniceae |
| 55 | Pistillate scales with narrow, indistinct bodies, scarcely enlarged at bases. | Carex sect. Squarrosae |
| 55 | Pistillate scales with wide, flat bodies, sometimes terminating in awns. | > 56 |
| 56 | Perigynium beak entire or emarginate. | > 57 |
| 56 | Perigynium beak with 2 distinct teeth at apex, usually at least 0.2 mm. | > 59 |
| 57 | Perigynium with not more than 5 veins extending length of body on abaxial face, veinless or weakly veined on adaxial face. | Carex sect. Hymenochlaenae |
| 57 | Perigynium with 8+ equally prominent veins on both faces. 58. Perigynia sharply angled in cross section. | Carex sect. Careyanae |
| 58 | Perigynia bluntly angled in cross section. | Carex sect. Laxiflorae |
| 59 | Pistillate spikes, at least the proximal, lax, proximal and middle perigynia separated by internodes at least 1/4 their length; leaves and sheaths not septate-nodulose. | Carex sect. Hymenochlaenae |
| 59 | Pistillate spikes dense, proximal and middle perigynia separated by internodes less than 1/10 their length; proximal leaves and sheaths sparingly septate-nodulose. | > 60 |
| 60 | Pistillate scales, at least proximal, awned, awn at least 1/4 of scale body length. | > 61 |
| 60 | Pistillate scales obtuse to acute or apiculate, apiculus not more than 1/10 of body length. | > 62 |
| 61 | Distal pistillate scales acuminate or with awn less than 1/2 body length; staminate spikes usually 2+. | Carex sect. Paludosae |
| 61 | Distal pistillate scales awned, awn usually more than 1/2 body length; staminate spikes 1, sometimes with 1 much smaller spike laterally. | Carex sect. Vesicariae |
| 62 | Culms purple-red at base; achenes with style persistent. | Carex sect. Vesicariae |
| 62 | Culms brown at base, without trace of red or purple; achenes with style deciduous. | Carex sect. Ceratocystis |
"shortened" is not a number.