3. Carex L. (sedge)

(Mackenzie, 1931–1935)

Plants perennial, monoecious or rarely dioecious, usually with short- or long-creeping rhizomes. Aerial stems 1 to many per plant, erect to arched or spreading, usually solid, unbranched, bluntly to sharply triangular in cross-section, glabrous or roughened, the plants sometimes producing separate fertile and vegetative stems. Leaves few to many, basal and often also alternate (3-ranked), with well-developed leaf blades or the lowermost leaves sometimes reduced to bladeless sheaths, the sheath with a scaly to papery ligule, the leaf blade spreading to ascending, flat or somewhat folded lengthwise, the margins sometimes inrolled. Inflorescences terminal and sometimes also in the upper leaf axils, composed of spikes, these 1 to many per stem, sessile or stalked, in spikes, racemes, or panicles, rarely in loose clusters or single. Spikes containing all staminate or all pistillate flowers or a mixture of both flower types; if a mixture then the staminate flowers either at the base of the spike or at the tip, often subtended by a sometimes reduced, leaflike bract, the flowers spirally alternate, usually dense, each subtended by a scale. Perianth (bristles or scales) absent. Staminate flowers with 3 stamens. Pistillate flowers with a single ovary, this loosely or tightly enclosed in (but not fused to) a perigynium (saclike structure ), this sometimes beaked or winged, and usually with 2 or more nerves. Styles not expanded at the base, not persisting on the fruit as a tubercle. Stigmas 2 or 3, protruding from a small opening at the tip of the perigynium. Fruits biconvex or 3-angled, sometimes somewhat flattened, enclosed in and shed with the perigynium. 1,500–2,000(–2,500) species, worldwide, most diverse in temperate to arctic regions.

Carex is the largest and arguably the most difficult genus in the Missouri flora. Species are sometimes separable consistently only by using technical characters of the spikes, scales, perigynia, and fruits. Flowering specimens may be impossible to determine with confidence. Characters of the rhizomes and vegetative stems may be important in species identification. For purposes of this treatment, perigynium length measurements include any beak present. The leaf sheath is often discussed as having two sides, the “dorsal” side, where the leaf blade is attached to the sheath, and the “ventral” side, opposite the leaf blade. Similarly, the perigynia, if flattened or otherwise differentiated into two sides, have the ‘dorsal’ (outer) side facing away from the axis of the spike and the ‘ventral’ (inner) side facing toward the center of the spike.

The basic unit of the Carex inflorescence is referred to as a spike or spikelet in the botanical literature. It is structurally different from the spike type of inflorescence found in various angiosperm families, as well as from the spikelets of the Poaceae or even other genera of Cyperaceae. In some species of Carex, the perigynium contains a reduced rachilla (axis) along the ovary. The perigynium thus can be interpreted as a bract that has become fused around a short inflorescence branch, which has been reduced to a single functional flower (Reznicek, 1990; Gleason and Cronquist, 1991). The term spike is used here for the sake of convenience and consistency with the majority of literature on the genus. The structures referred to as flowers (to avoid introducing more specialized terminology) in the genus also are unlike other flowers, in that they represent reduced inflorescence branches.

The genus usually is classified into four subgenera, Carex, Indocarex Baillon, Primocarex Kük., and Vignea (P. Beauv. ex T. Lestib.) Kük. The mainly Old World Indocarex grows only in the tropics, but the other three occur in Missouri. Some botanists do not distinguish subgenus Primocarex (in Missouri, only C. leptalea), which consists of various species groups in which the inflorescence contains only a single spike. Distinctions between these groups are complicated and rely upon combinations of inflorescence and flower characters. For our purposes, subgenus Vignea includes species with two stigmas and relatively short, sessile, lateral spikes usually containing both pistillate and staminate flowers. Subgenus Carex (subgenus Eucarex Coss. & Germ.) contains all of the species with three stigmas, as well as the C. aquatilis complex (section Phacocystis), which includes species with two stigmas in which most of the lateral spikes are elongate and contain only pistillate flowers.

Each of the subgenera of Carex has been further subdivided into a number of sections, which provide a more pragmatic level of classification at which to approach the study of the state’s sedges. Learning to recognize the common sections of Missouri sedges in the field can greatly simplify the process of determining species. The present treatment of Carex differs most markedly from that of Steyermark (1963) in the elimination of the single key to all sedge species, which proved difficult for many users to follow. Instead, the key to sections has been expanded, with separate keys to species at the beginning of each sectional treatment. The delimitations of sections and species are in general agreement with those in a forthcoming volume of the Flora of North America series, and were completed in consultation with A. A. Reznicek of the University of Michigan, who is helping to coordinate the production of Carex treatments for that work. The sectional classification differs somewhat from that of Steyermark (1963), but no attempt has been made in the present treatment to provide synonymy for sectional names.

The following key to the sections of Carex incorporates characters of leaves, stems, and pubescence where possible; thus several sections appear in more than one place in the key.