Cyperus diandrus, also known as umbrella flatsedge, is a species of flowering plant in the sedge familyCyperaceae. It is native to northeastern North America. It is sometimes confused with Cyperus bipartitus, both of which have chestnut-brown scales protecting the flowers. At one time, botanists considered the latter to be a variety of Cyperus diandrus.
Cyperus diandrus is an annualsedge with fibrous roots. There are multiple stems at the base of the plant. A stem rarely exceeds 25cm (9.8in) in height. Above the stem, the inflorescence bears clusters of spikelets, each with numerous florets. There are 2–3leaf-like bracts at the base of the inflorescence. The main cluster of spikelets at the top of the stem is stalkless, accompanied by 0–4additional clusters on stalks up to 6cm long. Each cluster supports 6–12flattened spikelets. The terminal spikelet is usually erect. A spikelet consists of 8–28florets, each covered by a scale (a type of bract in sedges and grasses). Each floret is bisexual with 2 (occasionally 3) anthers and a single style with two branched stigmas. The anthers and stigmas emerge from the axil of the floral scale but a perianth is absent. The fruit is an achene.[4][5]
Cyperus diandrus is sometimes confused with Cyperus bipartitus, both of which have pigmented floral scales ranging in color from reddish-brown to purplish-brown. The two species may be distinguished by the pigmented pattern on the surface of the scales.[5][6][7] Occasionally the scales will be entirely pale greenish-white.[8]Cyperus diandrus has conspicuous, persistent styles while those of Cyperus bipartitus are shorter and less conspicuous. The long styles of Cyperus diandrus give its spikelets a woolly appearance.
In 1813, the German-American botanist Frederick Traugott Pursh described a variety of Cyperus flavescens with chestnut-brown spikelets.[14] Pursh's description was based on specimens from New York, Vermont, and Massachusetts.[15] In 1836, Torrey published the name Cyperus diandrus var.castaneus based on Pursh's variety.[16] Torrey described a taxon with cespitose habit, shining dark-chestnut scales, and relatively short styles.[17][18]As of February2026[update], the name Cyperus diandrus var.castaneus(Pursh) Torr. is considered to be a synonym of Cyperus bipartitusTorr.[19]
Much exserted beyond the scales (2–4mm); three or four times the length of the achene; 2-cleft nearly to the base; straight
Scarcely exserted beyond the scales(<2mm); about twice the length of the achene; less deeply cleft; usually making a short double curvature toward the base
Cyperus diandrus is native to northeastern North America, ranging from Ontario and Nebraska to Nova Scotia and Virginia.[20] It was introduced in the state of Washington.[21] It grows on shorelines in sandy, peaty and slightly brackish habitats, usually not in disturbed areas.[4]
Ecology
Cyperus diandrus is a flowering plant whose season runs from July to October.[22]
↑Kartesz, John T. (2014). "Cyperusdiandrus". State-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). Retrieved 3 February 2026.
Kartesz, John T. (2014). "Cyperusdiandrus". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). Retrieved 3 February 2026.
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