The species name means "turned backward or downward" and refers to the perigynia of the spikelets that face downward when mature (Fernald 1950). A collection on Jones Beach Island in 2003 was the first time it had been seen on the island since 1935.
There are three existing populations but there is no information on population size from any one of them. There are three additional populations known, from 1899, the 1930s, and 1976 that have not been resurveyed although habitat still exists. There are eight populations that are extirpated due to loss of habitat.
None of the known populations have been rechecked so there is no information on short-term trends.
This plant has apparently always been rare as there have never been more than 20 known populations in the state. Its population numbers have declined over the long term as many of its sites in the New York City area have been destroyed.
Directed disturbance from the overuse of beaches and nearby swales and saltmarshes threatens this plant as does the invasion of Phragmites.
Beach and dune areas where it occurs should be protected from vehicle and human use. The Phragmites should be eliminated if it threatens populations.
Habitat preferences and reproduction success should be studied to understand how populations could be augmented at its present locations.
In New York this species has been collected from sandy coastal habitats including maritime dunes and the upper edges of a salt marsh. More information on the habitat requirements of this species in the state is needed (New York Natural Heritage Program 2010). Open woods and thickets in moist to dry, sandy soils (FNA 2002). Sandy barrens and coast (Gleason & Cronquist 1991).
This flatsedge is currently known from Queens and Suffolk counties. It was historically known from most of Long Island, Staten Island and Westchester County.
This flatsedge occurs along the Atlantic and Gulf coastal plain from Massachusetts and New York to Florida. It is also common inland from Virginia to Missouri and Oklahoma south to Texas.
Coast Flatsedge is a perennial, clump-forming, grass-like herb. Its stems are slender (up to 2 mm wide) 3-sided, or more or less rounded, and up to 50 cm tall. It has 3 to 6 V or W-shaped leaves that are 1.5 to 4 mm wide and up to 40 cm long. The infloresence consists of a single spike held on 4 to 8 rays (branches), up to 3.5 cm long, subtended by 4 to 6 ascending, rough-margined leafy bracts. There are 40 to 120 spikelets (each of 1 to 3 flowers) clustered into dense heads. The pistillate scales are persistent, appressed, straw-colored to brownish but green in the middle, with 3-4 ribs, and 1.8-2.5 mm long. The fruit are 3-sided, brown achenes 1.2 to 1.7 mm long (FNA 2002).
Distinguishing characteristics: perennial, ellipsoid-cylindric heads, lowest flowering scale 2-2.5 mm; stigmas three; achenes trigonous.
Mature fruit are needed for positive identification.
Cyperus echinatus has similar 3-sided achenes and few-flowered, dense heads, but differs by having large pistillate scales (lowest scale 3.5 to 4.3 mm versus 2 to 2.5 mm for C. retrorsus) and rounder heads (C. retrorsus has ellipsoid heads) (Gleason and Cronquist 1991).
Retrorse Flatsedge's fruit appears in late July and persists through October.
The time of year you would expect to find Retrorse Flatsedge fruiting in New York.
Cyperus retrorsus var. retrorsus None
Flora of North America Editorial Committee. 2002. Flora of North America, North of Mexico. Volume 23. Magnoliophyta: Commelinidae (in part): Cyperaceae. Oxford University Press, New York. 608 pp.
Fernald, M. L. 1950. Gray's manual of botany. 8th edition. Corrected printing (1970). D. Van Nostrand Company, New York. 1632 pp.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2021. New York Natural Heritage Program Databases. Albany, NY.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
Zaremba, Robert E. 1991. Corrections to phenology list of April 9, 1991.
This guide was authored by: Stephen M. Young
Information for this guide was last updated on: April 18, 2019
Please cite this page as:
New York Natural Heritage Program. 2021. Online Conservation Guide for Cyperus retrorsus var. retrorsus. Available from: https://guides.nynhp.org/retrorse-flatsedge/. Accessed July 29, 2021.