Digitaria ciliaris (Retz.) Koeler var. ciliaris, southern crabgrass. Annual (short–lived perennial herb), fibrous–rooted, to 12–stemmed at base, branched at lower nodes, spreading and decumbent, in range to 50 cm tall; shoots with basal leaves, cauline leaves, and prophylls; adventitious roots at nodes of stolonlike procumbent stems.
Stems (culms) cylindric but D–shaped to elliptic in ×–section at base of lateral branch (superficially appearing flattened with sheath enveloping both branches), < 2.5 mm diameter, light green becoming tannish or rose, internodes 25—85 mm long, often bent at nodes (geniculate), nodes glabrous or minutely puberulent (in range base of sheath short–hairy); internode hollow.
Leaves alternate distichous, simple with sheath; prophyll open, 2–keeled, 25—55 mm long, scabrous on keels and margins on lower surface, short–ciliate at base of margins; sheath open, 20—70 mm long (of flag leaf 60—120 mm long), < internode, not purplish above node or below blade, membranous on both margins, with veins raised on outer surface, glabrous (sparsely and finely puberulent above node or occasionally with papillate–based long hairs below collar), without lobes (auricles) at top; ligule membranous and broadly convex, 1—3(—4) mm long, semi–translucent and whitish to pale green, continuous with sheath margins, irregularly jagged on curved margin, glabrous or pilose above node; collar to 1.3 mm long, with wavy margin or margins, ± puberulent on back; blade narrowly linear–lanceolate, 45—105 × 5—9 mm, entire and minutely toothed on margins, narrowly acuminate at tip, parallel–veined with midrib on lower surface, in range with papillate–based hairs ca. 3 mm long at base.
Inflorescence spikelets, in terminal, ± umbel–like (subdigitate) panicles with 3—7 branches along rachis or appearing whorled, the branches (12—)25—120 × 0.5—1 mm, 1–sided with 2 stalked spikelets per node on lower side, spikelet of 2 florets but only upper one fertile, bracteate; peduncle 100—450 mm long, with pulvinus at top; rachis 1 mm long (1–branched) or 4.5—25 mm long (with 3—7 lateral branches), with densely pubescent nodes, having a pulvinus in axil of each lateral branch, the pulvinus bulbous, yellowish green or becoming purplish red; branches with raised whitish midvein and 3 green winged margins, wavy on margins; stalks at each node unequal, 0.4—0.6 mm and 1.1—4.5 mm long, free from midrib, 3–angled, scabrous.
Spikelet narrowly ovate, compressed top–to–bottom, breaking below glumes; glumes 2, lower glume appressed, ovate to triangular and semi–encircling, 0.3—0.4 mm long, opaque or translucent centrally, membranous on margins, veinless or sometimes appearing 2–veined or 3–veined with light green streaks; upper glume oblong to lanceolate, 1.7—2 × 0.7—0.8 mm, 3–veined, pale green with dark green veins, appearing windowlike (fenestrate), marginally with long and finely pilose–ciliate hairs spreading and separate at base and ascending and in contact with ends of neighboring hairs, pilose–ciliate between veins; lemmas 2, of sterile lower floret lanceolate to narrowly ovate, 2.3—2.7 × 1 mm, (5–)7–veined, light green with dark green veins, ciliate like upper glume, glabrous on back or pilose–ciliate between submarginal veins; of fertile upper floret lanceolate, 2.6—3.2 × 0.75—0.9 mm, light grayish green, glabrous, with colorless margins wrapped around palea and fruit, central vein glabrous with several minute scabrous teeth approaching tip, becoming very hard, finely striped; palea of upper floret lanceolate, 2 × 0.9 mm, light grayish green, not keeled, partially enveloping fruit, faintly 2–veined, finely striped
Flower bisexual; perianth (lodicules) 2, trapezoid to rectangular, 0.2—0.3 × 0.2—0.25 mm, truncate with 2 or 3 rounded teeth; stamens 3, free; filaments 2—3 mm long, white; anther exserted at tip of lemma, versatile, dithecal, 0.8—1.25 mm long, brownish yellow, yellowish, or whitish with purplish edges or red spots, arrow–shaped at base, longitudinally dehiscent; pollen light yellowish to colorless; pistil 1; ovary superior, lanceoloid, 0.5—0.8 × 0.25 mm, translucent yellowish green, 2–forked at top, 1–chambered with 1 ovule; styles 2, exserted at tip of lemma, 2—2.8 mm long, colorless, from thick base threadlike on basal 2/3, bottlebrushlike, arching, and pinkish purple aging purplish red from 0.6—0.9 mm to tip.
Fruit achene (caryopsis), enclosed within spikelet bracts, oblanceoloid somewhat compressed, 1.3—2.2 × 0.5—0.9 mm, creamy white to pale grayish green, opaque, flat on palea side and low convex on lemma side, with groove on 1 face; upper glume conspicuously ciliate, lemma and palea grayish green.
A. C. Gibson