Limnodea arkansana (Nutt.) L. H. Dewey, ozarkgrass. Annual, fibrous–rooted, often cespitose, (1—)several–stemmed at base, principal shoots unbranched above base, ± erect, in range to 45 cm tall; shoots with slender basal leaves withered at flowered and several wider cauline leaves.
Stems cylindric, node to 1.5 mm and internode < 1 mm diameter, internodes green to reddish and lower nodes sometimes aging reddish, internodes to 90 mm long; internodes hollow.
Leaves alternate distichous, simple with sheath; sheath open, tightly rolled and overlapping at base, low–ridged, < internode, green, pilose–ciliate on exposed margin and membranous on concealed margin, surface with inconspicuous microhairs, lacking lobes (auricles) at top; ligule membranous continuous from membranous margins, truncate and minutely jagged at top, 1—2 mm long, exposed surface minutely strigose with upward–pointing hairs; collar short; blade narrowly lanceolate–linear to linear, < 40—70 × 2—6 mm, the widest approaching midblade, with persistent hairs bases of pilose hairs + portions pilose–ciliate on margins, acuminate at tip, parallel–veined, veins pilose and with microhairs.
Inflorescence spikelets, in terminal, paniclelike array with spikelets on each branch spreading–ascending later strongly ascending, flowering portion narrowly lanceoloid in outline, to 120 × 22 mm but in fruit more narrow, having to 10 nodes, the lowest nodes or nodes somewhat hidden by persistent, suberect blade of flag leaf (sheath), spikelet having only 1 bisexual floret, awned; lateral branches to 4 per node, unequal, the longest to 40 mm long (incl. awns) and having 15+ spikelets, principal axes and branchlet axes nearly cylindric (never angled), green, with widely spaced, minute, scabrous hairs, axes often with somewhat swollen base, branchlets with 1—5 spikelets.
Spikelet scarcely compressed side–to–side, ca. 3 mm long + awn, with tips of glume > lemma, with erect glumes slightly gapping, breaking below glumes resulting in abscission of entire spikelet including 1 fruit; glumes 2, lacking awns, subequal, in range 3—3.3 mm long, green, 3–veined with lateral veins close to margins, in range short–hirsute and appearing minutely beaded on other cells, lower glume scarcely ridged (midvein), firm and persistent, tightly enclosing floret; rachilla above floret = fine bristle to 0.5 mm long persistent and appearing attached to lemma of floret; lemma sessile, 2–toothed at top with awn arising in notch, in range lemma body 2.7—2.9 mm long, < glume and appearing shorter in flower, rounded on back, membranous with 3 green veins, the outer surface minutely textured but glabrous, the teeth triangular, ca. 0.5 mm long, each green and having a lateral vein, the awn from notch initially mostly straight, in range 8—12.5 mm long, when mature strong twisted just above glumes and having a sharp bend near midpoint where awn diameter narrows (appearing 1–bent or 2–bent in developing fruit); palea membranous, narrow, 1.5—1.8 × 0.35—0.4 mm, < lemma and enclosed by lemma, colorless, if 2–keeled only to midpoint, veinless above keels, persistent.
Flower enclosed completely within floret; perianth (lodicules) 2, asymmetric lanceolate–ovate, ca. 1 × 0.35 mm, colorless and without veins, slightly swollen at base, with 1 straight margin, acute at tip, lacking hairs; stamens 3, free, 1 mm long; filaments ca. 0.6 mm long, colorless; anthers dorsifixed, dithecal, in range 0.4—0.45 mm long, pale yellow, longitudinally dehiscent; pollen yellowish; pistil 1, ca. 1 mm long; ovary superior, ovoid, ca. 0.3 mm long, white, 1–chambered with 1 ovule; styles 2, touching anthers, colorless, short–papillate (not bottlebrushlike).
Fruit achene (caryopsis), contained within awned spikelet (1 floret), ellipsoid somewhat compressed side–to–side, ca. 2 × 0.7 mm, smooth and opaque, dispersed when achene still fleshy and immature, in separated spikelet drying and aging brownish; lemma awn wavy below midpoint, mostly 8—12 mm long.
A. C. Gibson