1. Eleocharis acicularis (L.) Roem. &
Schult. (slender spike rush,
least spike rush)
Pl. 74 i, j; Map 274
E. acicularis f. fluitans
(Döll ex Glück) Svenson
E. acicularis f. longicaulis
(Desm.) Hegi
E. acicularis var. gracilescens
Svenson
Plants perennial, appearing tufted, often
forming mats, the tufts connected by slender, hairlike rhizomes (actually
stolons). Aerial stems 2–20(–40) cm long, 0.2–0.5 mm in diameter, 4–5-angled in
cross-section and usually finely ridged, lacking cross-lines. Basal sheaths
loose, reddish tinged toward the base, the tip membranous, truncate or slightly
oblique. Spikelets 2–6(–12) mm long, ovate-lanceolate to linear in outline,
pointed at the tip, with 1 sterile, basal scale. Scales 1.5–2.2 mm long,
ovate-lanceolate, pointed at the tip, with a green central area, a reddish
brown area on each side, and usually white-membranous margins. Perianth
bristles lacking or 3–4, slender, about as long as or somewhat shorter than the
fruits, usually not barbed. Stigmas 3. Fruits 0.7–1.0 mm long, the main body
elliptic-obovate in outline, slightly 3-angled to nearly circular in
cross-section, the surface with mostly 10–18 longitudinal ridges with numerous
fine cross-lines between them, white (rarely pale gray or light tan), shiny.
Tubercles short, narrowly conical-triangular. 2n=20, 30–38, 50–58.
July–October.
Scattered nearly throughout Missouri, commonest in the Ozarks (North America south to northern Mexico, Europe, Asia). Margins of ponds, lakes, sloughs, springs, and ditches, often colonizing
receding shorelines.
Mats of this species can grow so densely as
to inhibit the establishment of other aquatic species, and E. acicularis
has sometimes been seeded into small farm ponds to keep them from becoming
choked out with other, more robust aquatic plants. Although the species often
occurs along receding shorelines, it also grows well submerged. Such plants
sometimes have longer stems (to 40 cm long) and larger spikelets (6–12 mm
long). These ecotypes have been referred to as var. gracilescens and f. longicaulis
(Desm.) Hegi.