Tridens flavus (L.) Hitchc. var. chapmannii (Small) Shinn., greasegrass, fall redtop, purpletop tridens. Perennial herb, rhizomatous, fibrous–rooted, 1—several–stemmed at base, ascending with ascending to spreading inflorescences, in range < 100—165 cm tall; shoots with to 7 leaves above prophyll; rhizomes shallow, compact with short internodes.
Stems cylindric, to 5 mm diameter, internodes long with the longest 200+ mm long, nodes conspicuously purple; internodes hollow.
Leaves alternate distichous, simple with sheath; sheath open, tightly sheathing > 360°, finely ridged above midpoint, < internode, glossy purple at node, outer margin purplish membranous, of the lowest leaf often ± glaucous and sometimes purple; ligule densely membranous short–ciliate, 0.3—0.45 mm long; collar white with purplish margin, villous on outer surface; blade strap–shaped, mostly < 90—500 × 4.5—15 mm (of flag leaf < 50 mm long), the widest near base, minutely toothed on margins, long–tapered to tip, parallel–veined with veins raised as fine ridges on both surfaces.
Inflorescence spikelets, in terminal, open, paniclelike array, array ovate in outline, to 250 × 250 mm, overall appearing red–purple with spikelets aging purplish, lateral branches 2–compound with pulvinus in axil of each branch and branchlet, having widely spreading to ascending lateral branches in subopposite pairs or 1 per node spaced 15—25 mm along axis, principal branches to 130 mm long, spikelets not close to central axis, branchlets often descending with to 5 stalked spikelets, spikelets mostly with 6—8 florets often having a sterile floret at top, bracteate, conspicuously pilose on pulvinus; peduncle cylindric, < 100—300 mm long, smooth, fine–veined, glossy purple around node; bract subtending the lowest node appressed, tonguelike, ca. 1 mm long, with decurrent base; rachis somewhat irregularly low–ridged, axes slender, flexible, wiry, glossy green or blotched purple, pulvinus red–purple, pilose hairs to 1.5 mm long, white; stalk of spikelet 1—6 mm long.
Spikelet narrowly oblong in outline, (5—)7.8—9.5 mm long, breaking above glumes and between florets; glumes 2, unequal, 1–veined, lower glume ovate, ca. 2.5 mm long, keeled, purplish with green midvein, upper glume ovate, ca. 3.2 mm long, green; rachilla ca. 1 mm long, glabrous but with tuft of hairs at base of floret lemma; lemma angular, 2.7—4.8 mm long, green aging purplish, 3–veined with veins extended at tip (not convergent) as points along margin, points purple with upward–pointing barbs (awnlike but < 0.25 mm long, hairs sometimes purple; palea 2–keeled, = to slightly < lemma, somewhat stiff, folded along keels and concave between keels, with 2 awnlike points to 0.35 mm long, purplish, glabrous.
Flower bisexual, bilateral; perianth (lodicules) 2, free, short fan–shaped, ca. 0.3 mm long, white; stamens 3, free, exserted from floret; filaments slender, < 3 mm long, white; anthers dorsifixed, dithecal, 1—1.5 mm long, pale yellow; pollen whitish; pistil 1; ovary superior, oblong, ± 0.9 × 0.35—0.4 mm, pale green, glabrous, 1–chambered with 1 ovule; styles 2, from 2 spreading, conic bases at top of ovary, ca. 2 mm long above bases, white, feathery (plumose) and exserted at midfloret.
Fruit achene (caryopsis), enclosed in floret, ellipsoid slightly compressed front–to–back, 1.6—1.9 × 0.8—0.95 mm, dark brown, with 2 conic beaks.
A. C. Gibson