Cyperaceae

Growth Form and Habit

Mostly perennial herbs, often grass-like in appearance, typically growing from rhizomes or stolons, frequently forming dense clumps (cespitose) or extensive colonies (turf). Some species are annual.

Stems (Culms)

Aerial stems (culms) are characteristically solid (filled with pith, not hollow like most grasses) and often triangular in cross-section ("sedges have edges"), though round or flattened culms also occur. Nodes are generally not swollen.

Leaves

Leaves are typically arranged in three ranks (tristichous) along the base of the culm or along elongated vegetative stems. They consist of a closed sheath that encircles the culm (unlike the typically open sheath with overlapping margins in grasses) and a simple, linear blade with parallel venation. A ligule (appendage at the sheath/blade junction) may be present or absent. Basal leaves are common; culm leaves may be present or reduced/absent (Eleocharis).

Characteristic Cyperaceae features: Often triangular solid stem, 3-ranked leaves with closed sheaths.

Inflorescence

The basic unit of the inflorescence is the spikelet. Each spikelet contains one to many small flowers (florets), typically arranged spirally or distichously along a central axis (rachilla), with each floret subtended by a single scale-like bract (often called a floral scale or glume). Spikelets themselves are variously aggregated into larger inflorescences, such as single or multiple spikes, racemes, panicles, or dense head-like clusters (capitula). These larger inflorescences are often subtended by one or more leaf-like or scale-like involucral bracts.

Flowers (Florets)

Flowers are small, inconspicuous, highly reduced, and typically wind-pollinated (anemophilous). They are usually bisexual, but can be unisexual (plants then monoecious or dioecious, especially important in Carex).

• Perianth: Absent, or reduced to bristles, hairs, or small scales (typically 0-6 or more) located below the ovary and stamens. These persistent bristles can aid in fruit dispersal or identification.
• Androecium: Stamens usually 3 (sometimes 1, 2, or rarely 6+). Filaments are slender; anthers are typically basifixed (attached at the base) and dehisce via longitudinal slits.
• Gynoecium: Ovary is superior, composed of typically 2 or 3 fused carpels, forming a single locule (chamber) containing a single basal ovule. A single style arises from the ovary apex, bearing 2 or 3 elongated, often feathery or papillose stigma branches (the number usually matches the carpel number and predicts the fruit shape).
• Specialization in Carex: Flowers are strictly unisexual. The female flower (pistil) is uniquely enclosed within a sac-like or flask-shaped bractlet called the perigynium (or utricle). Only the style and stigmas protrude from the perigynium opening. The male flower typically consists of just 3 stamens subtended by a floral scale. Male and female spikelets can be separate or combined in various arrangements within the same inflorescence.

Left: Generalized Cyperaceae floret with scale, reduced perianth (bristles), stamens, superior ovary with styles. Right: Carex female flower enclosed in perigynium.

Fruits and Seeds

The fruit is characteristically a single-seeded, dry, indehiscent fruit called an achene (or sometimes nutlet). The shape of the achene is often diagnostic and typically reflects the number of carpels/stigmas: lens-shaped (biconvex) if derived from a 2-carpellate ovary (2 stigmas), or triangular in cross-section (trigonous) if derived from a 3-carpellate ovary (3 stigmas). The achene may be naked, subtended by persistent perianth bristles, or enclosed within the perigynium (Carex). The seed contains starchy endosperm and a small embryo.

Chemical Characteristics

Silica bodies are present in epidermal cells. Various secondary metabolites occur, including flavonoids and phenolic compounds. Cyanogenic glycosides are present in some. Alkaloids and iridoids are generally absent. C4 photosynthesis has evolved independently in several lineages within Cyperaceae (e.g., some Cyperus, Fimbristylis, Eleocharis), particularly those adapted to warm, high-light, or saline environments.