Plants perennial; cespitose or rhizomatous. Culms 60-400 cm, erect. Leaves not aromatic; basal and cauline; sheaths open, glabrous, margins scarious; auricles lacking; ligules membranous, ciliate; blades flat to conduplicate, glabrous or sparsely pubescent, margins scarious, sometimes scabrous. Inflorescences terminal and axillary, composed of a solitary, pedunculate rame; rames stout; disarticulation in the rames, below the sessile spikelets. Spikelets dorsally compressed, in heterogamous sessile-pedicellate pairs. Sessile spikelets embedded in the rame axes, ovate, with 2 florets, unawned; lower glumes indurate, smooth, rugose, or pitted, 7-11-veined, not keeled; upper glumes coriaceous, keeled, 1-veined; lower florets sterile; upper florets bisexual, unawned; anthers 3. Pedicels short, thick, appressed or partly fused to the side of the rame axes. Pedicellate spikelets 1-3 mm, usually reduced. Caryopses ellipsoid to broadly ellipsoid, yellow. x = 9. Name from the Greek koilos, hollow, and rachis, axis, in reference to the axes of the inflorescence, which are concave.

Racemes spike-like, cartilaginous, cylindric, the rachis readily disarticulating, each internode thickened distally and concave at its summit; spikelets paired, the fertile one sessile, closely appressed to the hollow of the adjacent internode, its first glume coriaceous and pitted or wrinkled; sterile spikelet smaller, its stout pedicel appressed to the rachis; smooth perennials; growing in small tufts, the slender solitary racemes resembling the pistillate portion of Tripsacum. 12, mainly trop.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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