Cyperus polystachyos Rottbøll. Coast Flatsedge. Phen: Jul-Oct. Hab: Low fields, ditches, and marshes. Dist: Pantropical and warm temperate, north in North America to ME, MA, KY, MO, and OK.

ID notes:Often difficult to separate from C. filicinus and occurring in similar habitats, although C. filicinus is generally more coastal. A highly polymorphic species; depauperate plants may resemble species in subgenus Cyperus, check carefully for 2-branched styles and biconvex achenes.

Origin/Endemic status: Native

Taxonomy Comments: A highly polymorphic species for which the infraspecific nomenclature should be examined critically: There are at least three infraspecific entities that R. Carter (pers.comm., 2022) refers to under the working names of C. polystachyos polystachyos, C. polystachyos hahnianus, and C. polystachyos texensis. Var. texensis is well known. It is a shorter plant than the others and is more widely distributed, occurring well beyond the coastal plain. C. polystachyos polystachyos is a much taller plant that appears to be restricted to the outer coastal plain – common throughout peninsular FL, northward into the FL panhandle, s GA, s AL, s MS, s LA, se TX (and probably in SC). C. polystachyos hahnianus is similar to C. polystachyos polystachyos in habit and most other respects except for the orientation of its spikelets: They are conspicuously fastigiate-pencilliform. In Florida, C. p. polystachyos and C. p. hahnianus do sometimes occur in mixed populations, which suggests that – as strikingly different as these plants are – C. p. hahnianus might better be treated as a form. Kükenthal’s description seems to match these plants going under the working name of C. p. hahnianus, and the type locality is Martinique (“insula Martinica”). However, I have not been able to access photographs of the type of Cyperus hahnianus Boeckeler, Flora 61: 138. 1878 [=Cyperus polystachyos var. hahnianus (Boeckeler) Kük.]. --Type: “Hahn. Herb. No. 700 – (Vidi in hb. reg. Berolin.) Insula Martinica.” -- Presumably at B.

Synonymy: = Ar, ETx1, FNA23, Il, Mex, NcTx, NE, Pa, Tn, Va; > Cyperus microdontus Torr. – S; > Cyperus odoratus L. – S, misapplied; > Cyperus paniculatus Rottb. – S; < Cyperus polystachyos Rottb. – GW1, WH3; > Cyperus polystachyos Rottb. var. holosericeus (Link) C.B.Clarke – K4; > Cyperus polystachyos Rottb. var. paniculatus (Rottb.) C.B.Clarke; > Cyperus polystachyos Rottb. var. texensis (Torr.) Fernald – Bah, C, F, G, K1, K3, Mo1, RAB, Tat, Tx, W

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Wetland Indicator Status:

• Atlantic and Gulf Coastal Plain: FACW
• Eastern Mountains and Piedmont: FACW
• Great Plains: FACW
• Midwest: FACW
• Northcentral & Northeast: FACW

Heliophily: 8