Eleocharis quadrangulata (Michx.) Roemer & Schult., square–stemmed spike–rush. Perennial herb, emergent aquatic, clonal, rhizomatous, fibrous–rooted, overall appearing cespitose, 1—several erect (leaning when flooded) shoots for each rhizome node, in range 40—90 cm tall (including submersed portion); shoots with prophyll and 2 basal leaves, glabrous, not glaucous; rhizomes horizontal, 2—3 mm diameter, white, internodes to 90 mm long, ensheathed by a firmly attached scale at each node = closed sheath, the scales alternate distichous, 6—11 mm long, white but with purple above midpoint and along split, with slender point at tip; adventitious roots several from base of each aerial shoot.
Stems (culms) submersed cylindric to rounded 3–sided, to 4 mm diameter, above water green and upper portion 3–sided (sterile shoot) or 4–sided (fertile shoot), internally spongy having a network of large air spaces (aerenchyma) with interrupted septa.
Leaves alternate, = bladeless sheath; prophyll nearly open and sheathing, triangular, < 70 mm long, white often with purplish red veins; sheaths closed, the lowest sheath to 90 mm long, free portion appearing acuminate–ovate to 7 mm long, white with purple veins, second sheath to 300—350 mm long, with many longitudinal veins and with vein bridges between them, white below water and greenish above water.
Inflorescence spikelet, solitary and terminal, splitting through leaf sheath, cylindric, > 20—40 × 2.5—3 mm, 40+–flowered, bracteate, bractlets (floral scales) helically alternate and shinglelike, the lowest 1—3 bractlets without flower, above each bractlet subtending a sessile flower, glabrous; peduncle = shoot length, green, approaching spike trapezoidal in ×–section with 2 ridges and channeled to bract tip; bract subtending spikelet (involucral bract), continuous with stem and not attached to rachis, nearly or completely sheathing, obtuse, to 2 mm long, thickly herbaceous and green with membranous margins, having many fine parallel veins on herbaceous portion, membranous margins to 1 mm wide, orangish between membranous margin and herbaceous base, obtuse at tip; first bractlet subtending aborted flower (lacking flower), to 4.5 mm long, ca. 15–veined; bractlet of fertile flower at least 1/2–encircling rachis, tightly appressed, ovate and cupping flower, 5—5.5 × 4 mm, light green in center, orangish between membranous margins and green tissue, vein not raised, obtuse to rounded at tip.
Flower bisexual, ± radial, sessile, mostly concealed by bractlet; perianth of 6—7 bristles fused in ring at base, unequal, 1—3 mm long some > fruit, colorless aging orangish, ascending and wavy, with backward–pointing short barbs and minute hook at tip, persistent during fruit development; stamens 3, free, included; filaments 0.6—0.8 mm long, white; anthers basifixed, dithecal, linear, 1.7—2.5 mm long, in range pale yellow (straw–colored), with appendage 0.2 mm long at tip, longitudinally dehiscent; pollen pale yellow; pistil 1; ovary superior, narrowly fusiform to ellipsoid, ± 0.6 mm long, green, 1–chambered with 1 ovule; style to 13 mm long, narrowly conic at base (0.3 mm) and distinct with a constriction above ovary aging as a tubercle, above tubercle unbranched ca. 4 mm long then (2—)3–branched, the branches with spreading short papillate hairs along entire length, stigmatic, ascending and mostly exserted from bractlet, slender, to 8 mm long, white.
Fruit achene having persistent tubercle (stylar) at top, 1–seeded, fruit body obovoid, ± 2.2 × 1.5 mm, glossy brown, minutely pebbly on surface with pits (collapsed cells) in longitudinal rows; tubercle ca. 0.5 × 0.4—0.5 mm, brown, ± wrinkled.
A. C. Gibson