2. Schoenoplectus americanus (Pers.) Volkart ex Schinz & R. Keller (saltmarsh bulrush, Olney three-square)

Pl. 81 a, b; Map 306

Scirpus americanus Pers.

Scirpus olneyi A. Gray

Plants perennial with stout, long-creeping rhizomes. Stems widely spaced on the rhizomes, 50–150 cm long, stiff, strongly triangular in cross-section, the sides usually noticeably concave when fresh (difficult to see when pressed). Leaves 2–4 near the stem bases, the lowermost 1–3 reduced to bladeless sheaths, the other 1–3 with leaf blades 3–20 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 2–15 spikelets in a sessile, headlike cluster, the bract 1, 1–6 cm long, other, reduced bracts absent. Spikelets 6–15 mm long, ovate in outline, rounded to bluntly pointed at the tip. Spikelet scales 3.5–6.0 mm long, broadly ovate, shallowly notched at the tip, orangish brown to brown, often tinged with purple, the green or straw-colored midrib extended past the main body of the scale as a short awn. Perianth bristles (3–)4–6, shorter than to slightly longer than the fruits, relatively stout and straight or slightly curved or arched around the fruit, retrorsely barbed. Stigmas 2. Fruits 1.8–2.5 mm long, obovate in outline, somewhat flattened, unequally biconvex in cross-section, the surface smooth or nearly so, yellow, turning greenish brown and eventually dark brown, shiny. 2n=78. June–September.

Uncommon and possibly extirpated, known only from a single historical collection from Jefferson County (U.S. and adjacent Canada, south to South America). Alkaline seeps, sometimes in shallow water.

Schoenoplectus americanus was long known as Scirpus olneyi because of confusion as to the application of the former name. It is more common to the west of Missouri and often occurs in strongly alkaline soils. Because winter application of road salt has turned soils along many highways more alkaline, it is possible that this species may become more common in the state in the future. Where S. americanus occurs with S. pungens, sterile hybrids are sometimes formed. These are known as S. ×contortus (Eames) T. Koyama and have not yet been reported from Missouri. The hybrids bear a morphological resemblance to S. deltarum (see further discussion under the treatment of that species).