Cyperus bipartitus f. elongatus(Boeckeler) Mohlenbr.
Cyperus bipartitus f. elutus(C.B.Clarke) Mohlenbr.
Cyperus castaneusBigelow
Cyperus diandrus var. castaneus(Pursh) Torr.
Cyperus flavescens var. bicolorFarw.
Cyperus flavescens var. castaneusPursh
Cyperus lagunettoSteud.
Cyperus niger var. rivularis(Kunth) V.E.Grant
Cyperus pauperPhil.
Cyperus rivularisKunth
Cyperus rivularis var. acutatusC.B.Clarke
Cyperus rivularis f. acutatus(C.B.Clarke) Kük.
Cyperus rivularis var. depauperatusC.B.Clarke
Cyperus rivularis f. depauperatus(C.B.Clarke) Kük.
Cyperus rivularis var. elongatusBoeckeler
Cyperus rivularis var. elutusC.B.Clarke
Cyperus rivularis f. elutus(C.B.Clarke) Kük.
Cyperus rivularis subsp. lagunetto(Steud.) Kük.
Cyperus rivularis var. lagunetto(Steud.) O'Neill
Cyperus rivularis f. subacaulisKük.
Cyperus tenuiculusKunth
Pycreus lagunetto(Steud.) C.B.Clarke
Pycreus rivularis(Kunth) Palla
Cyperus bipartitus, also known as slender flatsedge, river cyperus, or shining flatsedge, is a species of flowering plant in the sedge familyCyperaceae. It is native to the Americas, from southeastern Canada to northern Argentina. One of its common names refers to the shining dark-chestnut scales protecting the flowers. It is sometimes confused with Cyperus diandrus, both of which have chestnut-brown floral scales. It is not to be confused with Cyperus gracilis, another species known as "slender flatsedge".
Cyperus bipartitus 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 3cm long. Each cluster supports 3–10flattened spikelets. The terminal spikelet is usually erect. A spikelet consists of 10–26florets, each covered by a scale (a type of bract in sedges and grasses). Each floret is bisexual with 2–3anthers 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, a black disc about a millimeter wide.[5][6][7]
Cyperus bipartitus is sometimes confused with Cyperus diandrus, both of which have pigmented floral scales, ranging in color from reddish-brown to purplish-brown. The two species may be distinguished by the pattern of pigmentation in the scales,[8][9] but occasionally the scales will be entirely pale greenish-white.[10]Cyperus diandrus has conspicuous, persistent styles while those of Cyperus bipartitus are shorter and less conspicuous.
Taxonomy
Cyperus bipartitus was named and described by the American botanist John Torrey in 1836.[3] Torrey's description was based on a specimen collected in New Orleans, Louisiana.[11][12] A year later, the German botanist Carl Sigismund Kunth named and described Cyperus rivularis based on a specimen collected in the U.S.state of Georgia.[13] Both names remained in use for more than 150years until Cyperus rivularisKunth was placed in synonymy with Cyperus bipartitusTorr.[14]As of February2026[update], the latter is a widely accepted name.[4][15][16][17][18]
In 1813, the German-American botanist Frederick Traugott Pursh described a variety of Cyperus flavescens with chestnut-brown spikelets.[19] Torrey, having named and described Cyperus diandrus in 1819,[20] published the name Cyperus diandrus var.castaneus based on Pursh's variety.[21] In 1836, Torrey described a taxon with cespitose habit, shining dark-chestnut scales, and relatively short styles.[22] He noted the taxon was commonly found in New England and western New York State. As of February2026[update], both Cyperus flavescens var.castaneusPursh and Cyperus diandrus var.castaneus(Pursh) Torr.are considered to be synonyms of Cyperus bipartitusTorr.
Torrey simultaneously published the names Cyperus diandrus var.castaneus and Cyperus bipartitus in 1836. Both Cyperus diandrus and Cyperus bipartitus have bifid styles (two stigmas),[10][23] but Torrey included the latter with a group of species with three stigmas. A century later, the German botanist Georg Kükenthal responded to the error by reducing Cyperus bipartitus to a variety of Cyperus diandrus.[24][25]As of February2026[update], the name Cyperus diandrus var.bipartitus(Torr.) Kük. is considered to be a homotypic synonym of Cyperus bipartitusTorr.
Distribution and habitat
Cyperus bipartitus is native to the Americas, from southeastern Canada to northern Argentina.[4] It is found in wet environments such as lakes, sandbars, and ditches at elevations to 1,500 metres (4,900ft).[5]
↑Kartesz, John T. (2014). "Cyperusbipartitus". State-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). Retrieved 2 February 2026.
↑Kartesz, John T. (2014). "Cyperusbipartitus". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). Retrieved 2 February 2026.
Tucker, Gordon C. (1983). "The Taxonomy of Cyperus (Cyperaceae) in Costa Rica and Panama". Systematic Botany Monographs. 2: 1–85. doi:10.2307/25027589. JSTOR25027589.
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