12. Eleocharis wolfii A. Gray (Wolf’s spike rush)

Pl. 74 g, h; Map 285

Plants perennial, appearing sparsely tufted, often forming mats, the tufts connected by slender, hairlike rhizomes. Aerial stems 10–30(–40) cm long, 0.7–1.2 mm in diameter, strongly flattened and finely ridged, often somewhat inrolled, lacking cross-lines. Basal sheaths loose, tinged reddish purple toward the base, the tip membranous, somewhat oblique. Spikelets 5–10 mm long, ovate-lanceolate in outline, pointed at the tip, with 2 or 3 sterile, basal scales. Scales 2.5–3.0 mm long, ovate-lanceolate, pointed and often tapered at the tip, with a green or straw-colored central area, a broad purplish brown area on each side, and green or white-membranous margins. Perianth bristles lacking. Stigmas 3. Fruits 0.7–1.0 mm long, the main body narrowly obovate in outline, slightly 3-angled to nearly circular in cross-section, the surface with 6–10 longitudinal ridges with numerous fine cross-lines between them, white (rarely pale gray or light tan), shiny. Tubercles narrowly conical. May–July.

Uncommon, known only from Callaway and Linn Counties (eastern U.S. and adjacent Canada west to Colorado). Wet depressions of bottomland and mesic upland prairies.

This species is frequently confused with E. acicularis, which also forms tufted mats and has hairlike rhizomes. However, the broader, flattened aerial stems (vs. 4–5-angled) and longer spikelet scales distinguish the two. Fruits of these two species can be indistinguishable.

Eleocharis wolfii has not been seen in Missouri in recent years and may be extirpated from the state. However, searches in Illinois have resulted in the discovery of a number of populations there, and it may be that Missouri populations have simply been overlooked in the field.