Schoenoplectus heterochaetus was included in Michigan Flora, Vol. 1 and the Field Manual (plus earlier versions of this website) based on two specimens labeled as having been collected at Lansing (or the Agricultural College), Ingham Co. (without collector, in 1871, MSC). As these two sheets also have no habitat and specific date, and the species has never been seen elsewhere in the State, it seems likely that there was a label mix-up. We have therefore deleted S. heterochaetus from the flora. If found it would resemble S. acutus or S. tabernaemontani, but would differ in having 3-cleft styles (not 2-cleft), perianth bristles only 2–4 (–5), not 6, and in aspect by bearing most of the spikelets singly on long, flexuous pedicels, rather than having spikelets borne largely in groups of 2–7.
1. Spikelets (at least several of them) distinctly pediceled (sometimes congested in S. acutus); culms terete, often over 1 m tall.
2. Culms firm and dark olive-green when fresh; spikelets ovoid to cylindrical (often 2.5 or more times as long as wide), usually in a stiffer, sometimes condensed, inflorescence; scales dull, pale or whitish brown, the midrib not strongly contrasting, the margins often more copiously ciliate than in S. tabernaemontani, and the backs copiously flecked with shiny red dots, often puberulent; mature achenes ca. 2.2–2.7 mm long, including apiculus, completely hidden by the scales.
2. Culms rather soft and easily compressed, pale blue-green when fresh; spikelets ovoid (about twice as long as wide, or shorter), in an open, lax inflorescence; scales ± shiny, rich orange-brown, often with prominent greenish midrib, the margins ciliate but the backs essentially glabrous (puberulence and swollen red flecks, if any, limited to region of midrib); mature (dark gray or lead-colored) achenes ca. 1.6–2.1 (–2.4) mm long, including apiculus, barely covered by the scale.
1. Spikelets 1-few, crowded, sessile or nearly so (rarely one on a short pedicel); culms 3-angled or terete (if terete, then slender, soft, and not over 1 m tall).
3. Spikelet 1, strongly ascending, the involucral bract surpassing its tip by not more than 15 (–20) mm; leaves normally many, hair-like, submersed; culm seldom over 1 mm thick; anthers (2.1–) 2.5–3.5 mm long; achenes 3-sided, the body ca. 2.5–3 mm long.
3. Spikelets usually more than 1 and the involucral bract surpassing them by more than 15 mm (except in smallest plants of some populations); leaves stiff and culms thicker; anthers and achenes various.
4. Midrib of scale ± greenish, excurrent as a short (not over 0.5 mm) tip extending beyond the tapered (sometimes very slightly notched) apex of the scale; bristles slightly exceeding body of achene; rhizome soft; achene with apiculus 0.5 mm or more in length; styles 3-cleft and achenes 3-sided; leaves more than half as tall as the culms.
4. Midrib of scale brown, excurrent either as a very short tip not exceeding the broad lobes at apex of scale or as a long (0.5–1 mm) tip equaling or exceeding lobes; bristles shorter than body of achene; rhizome firm and hard; achene with apiculus shorter than 0.5 mm; styles usually 2-cleft and achenes biconvex to plano-convex (occasionally some styles 3-cleft and achenes 3-sided in a spikelet); leaves less than half as tall as the culms.
5. Scales with excurrent tip less than 0.5 mm long, equaling or shorter than lobes at apex of scale; culms soft, very sharply 3-angled or -winged; anthers and achenes slightly smaller than in S. pungens; involucral bract up to 5 cm long, usually shorter; local in salt marshes.
5. Scales with firm excurrent tip ca. 0.5–1 mm or more long, usually exceeding lobed apex of scale; culm firm, 3-angled but not winged; anthers (1.7–) 2–3 mm long (including short scabrous tip); body of achene (2.3–) 2.5–3 mm long; involucral bract 3.5–11 (–15) cm long; common in wet ground.