8. Schoenoplectus pungens (Vahl) Palla (chairmaker’s rush, common three-square)

Pl. 81 e–g; Map 312

Scirpus pungens Vahl

Plants perennial with stout, long-creeping rhizomes. Stems widely spaced on the rhizomes, 30–200 cm long, stiff, strongly triangular in cross-section, the sides flat to slightly concave when fresh. Leaves 2–4 near the stem bases, the lowermost 1–3 reduced to bladeless sheaths, the other 1–3 with leaf blades 3–40 cm long, these thick, V-shaped to flattened-triangular in cross-section. Leaf sheaths oblique at the tip with a U-shaped sinus on 1 side. Inflorescences of 1–4(–10) spikelets in a sessile, headlike cluster, the bracts 2–3, the main bract (1–)5–20 cm long, the others much reduced and scalelike. Spikelets 5–22 mm long, ovate to narrowly elliptic in outline, mostly pointed at the tip. Spikelet scales 4–6 mm long, ovate to narrowly ovate, shallowly notched at the tip, orangish brown to brown, sometimes with reddish purple spots or streaks, the green or straw-colored midrib extended past the main body of the scale as a short awn. Perianth bristles (3–)4–6, as long as or shorter than the fruits, relatively stout and straight or slightly arched around the fruit, retrorsely barbed. Stigmas 2 or occasionally 3. Fruits 2.2–3.3 mm long, mostly more than 2.5 mm long, obovate in outline, somewhat flattened, unequally biconvex or occasionally slightly triangular in cross-section, the surface smooth or slightly roughened, yellow, turning greenish brown and eventually dark brown, somewhat shiny. 2n=74, 76, 78. May–September.

Scattered nearly throughout Missouri, but more common south of the Missouri River (U.S. and adjacent Canada south to South America and the Caribbean Islands; Europe, Australia). Margins of ponds, lakes, sloughs, and ditches, gravel bars, and stream banks, fens, and marshes, sometimes in shallow water.

This species was long-known as Scirpus americanus in the literature, before Schuyler (1974) determined that the epithet americanus instead belonged to plants called S. olneyi by various authors. The S. pungens complex is a confusing group of closely related species, of which the most widespread and morphologically variable is S. pungens and its several varieties and subspecies. Other Missouri members of the complex include S. deltarum and S. americanus, which can be distinguished by the relatively subtle characters in the key to species above. See the treatment of S. deltarum for further discussion of rare intermediates between these species. Within S. pungens, two weakly separable varieties occur in Missouri.