Schoenoplectus americanus (Persoon) Volk ex Schinz & R. Keller. Olney Threesquare. Phen: Late May-Jun; Jun-Sep. Hab: Tidal freshwater to brackish marshes. Dist: NS west to WA, south to South America.

ID notes: The leafless stems of Schoenoplectus americanus are sharply triangular in cross-section and grow 1-2 meters tall. Near the summit of each stem is a single compact cluster of spikelets, with an erect bract that looks as if it were a continuation of the stem. It is very much like S. pungens, but the color of S. americanus is brighter green, the stems are sharply triangular (vs. much less sharply angled in that species), and the inflorescence bracts are shorter (1-6 cm long vs. 3-20 cm long).

Origin/Endemic status: Native

Taxonomy Comments: Schuyler (1974) discussed the need to replace the name S. olneyi (as traditionally applied) with S. americanus, traditionally applied to what must now be called S. pungens. Because of this nomenclatural change, the interpretation of much information and records is now uncertain.

Synonymy ⓘ: = ETx1, FNA23, GrPl, Il, K1, K3, K4, Mex, Mi, Mo1, NE, NY, Va, WH3, Strong (1994); = Scirpus americanus Pers. – C; = Scirpus olneyi – F, G, GW1, RAB, S, S13, Tat, Tx

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Wetland Indicator Status:

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

Heliophily ⓘ: 8