10. Schoenoplectus saximontanus (Fernald) J. Raynal (Rocky Mountain bulrush)

Pl. 82 c, d; Map 314

Scirpus saximontanus Fernald

Scirpus supinus L. var. saximontanus (Fernald) T. Koyama

Plants annual or apparently so, the rhizomes absent or very short and hidden by the aerial stem bases. Stems tufted, 4–40 cm long, stiff, circular in cross-section to slightly flattened, sometimes appearing longitudinally ridged when dry. Leaves 2–3 near the stem bases, all but the uppermost reduced to bladeless sheaths, this with the leaf blade 0.5–8 cm long, C-shaped to flattened in cross-section. Leaf sheaths oblique at the tip with a V-shaped sinus on 1 side, usually split open, the margins of the split transparent and membranous, often becoming somewhat shredded with age. Inflorescences of 1–10 spikelets in a sessile, headlike cluster (rarely a second, short-stalked cluster also present), the bracts 1–2, the main bract 3–16 cm long, the other much reduced and scalelike. Individual 1-flowered spikelets also sometimes present at the base of the stem, usually obscured by the encircling leaf sheath. Spikelets 5–16 mm long, ovate to lanceolate or narrowly elliptic in outline, rounded to pointed at the tip. Spikelet scales 2.5–4.0 mm long, ovate, tan to orangish brown, papery to membranous, the green or straw-colored midrib tapered past the main body of the scale into a short, sharp point. Perianth bristles usually absent, rarely 1–2 present in basal flowers, these as long as or shorter than the fruits, relatively slender, straight to contorted or bent, retrorsely barbed. Stigmas 3. Fruits 1.3–1.7 mm long (slightly larger in fruits of basal spikelets), obovate to broadly elliptic in outline, 3-angled in cross-section, the surface with a fine series of irregularly undulating, horizontal ridges, dark brown to black, shiny. 2n=50. July–September.

Uncommon, known only from Platte and St. Charles Counties in the Missouri and Mississippi River floodplains (western U.S. east locally to Ohio). Mudflats and sandy depressions of marshes.

This species was first reported for Missouri by Schuyler (1969) and Castaner (1984), and the oldest collection from the state (without further locality data) was cited as having originated in 1848. It is becoming more common in the eastern portion of its range and is apparently being spread by migrating waterfowl. It shares with S. hallii the unusual character of amphicarpy, the production of individual florets wrapped in the leaf sheaths at the stem bases (noticeable only by the long style protruding from the tip of the leaf sheath).