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Rhizomatous, perennials herbs. Rhizome short, horizontally creeping, knotty. Leaves basal, 3-ranked; blades elongated or reduced, ligules absent. Involucral bracts leaf like. Inflorescence capitate. Spikes 1-few, sessile, cylindric, ellipsoid or globose, axil short. Spikelets numerous, falling entire, crowded, bilaterally flattened. Glumes several, 2-ranked, laterally flattened, sides membranous to hyaline, keel strongly acute, sometimes winged, smooth, spinulate or serrulate. Flowers 1-5 per spikelet, bisexual or staminate in upper glumes. Perianth segments absent. Stamens 2-3. Stigmas 2, style continuous with ovary. Nutlets 1-2 per spikelets, laterally biconvex.

Key to the species

Serial Key Reference
1a. Glumes abaxially keeled K. nemoralis
1b. Glumes not abaxially keeled 2
2a. Rhizomes short; culms tufted; spikes (1-)3; glume abaxial keel without spinules 3
2b. Rhizomes short; culms scattered, single at each node of rhizome; spikes 1(-3); glume abaxial keel spinules 5
3a. Middle spike broadly ovoid, 5-6 mm diameter; lateral spikes globose, 3-4 mm diameter; spikelets oblong, 1-flowered K. bulbosa
3b. Middle spike oblong-culindric to oblong, 7-14 mm diameter; lateral spikes oblong, 5-6 mm diameter; spikelets ovoid-ellipsoid to ovoid, 1- or 2-flowered 4
4a. Plants perennial; spikes whitish; achenes with whitish stipitate base K. odorata
4b. Plants annual; spikes pale greenish; achenes light brown K. pumila
5a. Stigmas 2; nutlets yellowish-brown at maturity K. brevifolia
5b. Stigmas 3; nutlets black at maturity K. microcephala