Cyperus diandrus

Cyperus diandrus
North shore of Lake Ontario, Canada in August
Secure
Secure  (NatureServe)[1]
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Cyperaceae
Genus: Cyperus
Species:
C. diandrus
Binomial name
Cyperus diandrus
Synonyms[3]
Homotypic synonyms
    • Pycreus diandrus (Torr.) C.B.Clarke
    • Torreya maritima Raf.
Heterotypic synonyms
    • Cyperus diandrus f. elongatus (Britton) Fernald
    • Cyperus diandrus var. elongatus Britton
    • Cyperus diandrus var. pauciflorus Alph.Wood

Cyperus diandrus, also known as umbrella flatsedge, is a species of flowering plant in the sedge family Cyperaceae. 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.

Description

Cyperus diandrus is an annual sedge with fibrous roots. There are multiple stems at the base of the plant. A stem rarely exceeds 25 cm (9.8 in) in height. Above the stem, the inflorescence bears clusters of spikelets, each with numerous florets. There are 2–3 leaf-like bracts at the base of the inflorescence. The main cluster of spikelets at the top of the stem is stalkless, accompanied by 0–4 additional clusters on stalks up to 6 cm long. Each cluster supports 6–12 flattened spikelets. The terminal spikelet is usually erect. A spikelet consists of 8–28 florets, 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]

Cluster of spikelets (New York in Sep)

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.

Spikelet with florets (Quebec in Sep)
Floret and achene with persistent style

Taxonomy

Cyperus diandrus was named and described by the American botanist John Torrey in 1819.[2] Its type specimen was collected in salt marshes near New York City.[9] Torrey referred to the species as the "diandrous galingale".[10] As of February 2026, the botanical name Cyperus diandrus Torr. is widely accepted.[3][11][12][13]

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 February 2026, the name Cyperus diandrus var. castaneus (Pursh) Torr. is considered to be a synonym of Cyperus bipartitus Torr.[19]

Cyperus diandrus Cyperus bipartitus
(syn. Cyperus diandrus var. castaneus)
Spikelets Flatly compressed Less so
Scales, shape Oblong, with obtuse tips Longer and narrower, very closely imbricated (overlapping)
Scales, pigment Thin band of pigment along the margin, with a conspicuous pale area on the face of the scale More heavily pigmented such that a pale area is lacking
Scales, texture Membranaceous (thin, pliable) Coriaceous (leathery), with a firmer texture
Styles Much exserted beyond the scales (2–4 mm); three or four times the length of the achene; 2-cleft nearly to the base; straight Scarcely exserted beyond the scales(<2 mm); about twice the length of the achene; less deeply cleft; usually making a short double curvature toward the base
Achenes Oblong-obovate, slightly scabrous, dull Orbicular-obovate, minutely wrinkled transversely

Distribution and habitat

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]

Conservation

As of February 2026, the NatureServe global conservation status of Cyperus diandrus is secure (G5).[1] It is imperiled (S2) in Pennsylvania.[23]

See also

References

  1. ^ a b NatureServe (30 January 2026). "Cyperus diandrus". NatureServe Explorer. Arlington, Virginia. Retrieved 3 February 2026.
  2. ^ a b "Cyperus diandrus Torr.". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew; Harvard University Herbaria & Libraries; Australian National Botanic Gardens. Retrieved 3 February 2026.
  3. ^ a b "Cyperus diandrus Torr.". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 3 February 2026.
  4. ^ a b Tucker, Gordon C.; Marcks, Brian G.; Carter, J. Richard (2002). "Cyperus diandrus". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). Vol. 23. New York and Oxford: Oxford University Press. Retrieved 3 February 2026 – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  5. ^ a b "Cyperus diandrus (Umbrella Flatsedge)". Minnesota Wildflowers. Retrieved 4 February 2026.
  6. ^ "Comparison of Cyperus bipartitus and Cyperus diandrus spikelets". Minnesota Wildflowers. Retrieved 3 February 2026.
  7. ^ "Cyperus diandrus — umbrella flatsedge". Go Botany. Native Plant Trust. Retrieved 3 February 2026.
  8. ^ Reznicek, A. A.; Voss, E. G.; Walters, B. S. (February 2011). "Cyperus". Michigan Flora Online. University of Michigan. Retrieved 2 February 2026.
  9. ^ Torrey (1819), p. 90.
  10. ^ Torrey (1843), pp. 338.
  11. ^ "Cyperus diandrus Torr.". WFO Plant List. Retrieved 4 February 2026.
  12. ^ "Cyperus diandrus Torrey". Database of Vascular Plants of Canada. Retrieved 4 February 2026.
  13. ^ NRCS. "Cyperus diandrus". PLANTS Database. United States Department of Agriculture (USDA). Retrieved 4 February 2026.
  14. ^ "Cyperus flavescens var. castaneus Pursh". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew; Harvard University Herbaria & Libraries; Australian National Botanic Gardens. Retrieved 14 February 2026.
  15. ^ "Cyperus flavescens var. castaneus Pursh". Global Biodiversity Information Facility. Retrieved 16 February 2026.
  16. ^ "Cyperus diandrus var. castaneus (Pursh) Torr.". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew; Harvard University Herbaria & Libraries; Australian National Botanic Gardens. Retrieved 9 February 2026.
  17. ^ Torrey (1836), pp. 251–2.
  18. ^ Torrey (1843), pp. 338–339.
  19. ^ "Cyperus diandrus var. castaneus (Pursh) Torr.". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 9 February 2026.
  20. ^ Kartesz, John T. (2014). "Cyperus diandrus". State-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). Retrieved 3 February 2026.
  21. ^ "Cyperus diandrus (umbrella flatsedge)". Burke Herbarium. Retrieved 10 February 2026.
  22. ^ "Cyperus diandrus Torrey". Flora of the Southeastern United States. Retrieved 3 February 2026.
  23. ^ "Umbrella Flatsedge Cyperus diandrus" (PDF). Pennsylvania Natural Heritage Program. Retrieved 10 February 2026.

Bibliography

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