Tripsacum dactyloides (L.) L., eastern gamagrass. Perennial herb, rhizomatous, fibrous–rooted, cespitose, many–stemmed at base, with principal shoots ascending, in range 130—180 cm tall; monoecious; shoots with basal leaves and cauline leaves, basal leaves with blades to 1250 mm long, below midblade folded upward from midrib somewhat V–shaped, cauline leaves with blades shorter and broader, blade of flag leaf acuminate–lanceolate and as small as 65 × 7 mm, scabrous; rhizome creeping, shallow, the thickest 13+ mm diameter, tough and hard, hidden by persistent, fibrous sheaths of older leaves, the sheaths conspicuously alternate distichous, with thick adventitious roots emerging from lower side of rhizome.
Stems ± elliptic in ×–section to 7 × 4 mm, glabrous; internodes solid.
Leaves alternate distichous, simple with sheath; prophyll (most easily observed on axillary reproductive shoot) strongly 2–keeled and with margins folded and long–tapered to tip, open, to 165 × 4—5 mm (folded), keels membranous, ⊥ from surface, 0.5—0.6 mm wide, and scabrous, colorless between keels and green on wide, folded margins; sheath open, of basal and lower cauline leaves keeled (from midrib), to 225 mm long, strongly folded upward and V–shaped, and whitish belowground, of other cauline leaves wrapped > 360° and to 150 mm long and green, without lobes (auricles) at top; ligule membranous, truncate, < 1 mm long, short–ciliate on margin, on surface facing blade conspicuously appressed hirsute; blade strap–shaped long–tapered to tip, of basal leaves < 600—1250 mm long, of cauline leaves mostly 400—780 × 11—21 mm, the widest below midblade, minute teeth on margins, parallel–veined with whitish midrib raised on lower surface, with minute teeth along principal veins on lower surface and several on upper surface.
Inflorescence spikelets, unisexual, in terminal spikes and appearing axillary from upper cauline nodes, axillary spike terminal on short shoots with prophyll and a flag leaf, in range spikes solitary or 2–branched, each spike cylindric, 130—250 mm long, having spikelets conspicuously alternate distichous, spikelets 1–flowered, basal 4—8 nodes having 1 pistillate spikelet per node, tightly fused at node and nested within a cavernlike internode (rame segment), arching staminate upper portion of spike (above pistillate segments) having to 25 nodes each with 2 fully exposed staminate spikelets, of the pair the lower spikelet sessile and upper spikelet subsessile, staminate spikelets 4–ranked, approaching tip 2—4 nodes with only 1 spikelet (staminate, sterile, or neuter), bracteate; after pollination staminate portion abscised from spike, leaving the erect stack of pistillate rame segments (often without developing fruits); rame segments of pistillate portion 6—8(—9.5) mm long, of staminate portion internodes 6—8 × 1.4—1.6 mm, with short, ascending stiff hairs along edges, staminate spikelets often tinged purple–red.
Pistillate spikelet on axis easily broken into segments and shattering later as dispersal units; spikelet mostly embedded in rame segment, ovoid, 9.5—11 × 4.5 mm, typically > rame segment with tip overlapping next segment, on outer side at base rame segment margins with ciliate notch having hairs 1 mm long, bracts alternate distichous; glumes 2, lower glume visible, sheathing spikelet, tough aging hard, glossy green and glabrous or a tuft of minute hairs at tip, upper glume with sheathing 2×, < lower glume, pale green, not hard; lemma membranous, sheathing forming conic structure, acute, ca. 7 × 7 mm, translucent, veins fine and inconspicuous except approaching tip; palea membranous, 2–keeled approaching tip, unfolded roundish and ca. 5 × 5 mm and shallowly notched at tip, the folded margins wide so palea appearing ca. 2 mm across, the teeth 0.4—0.6 mm long.
Pistillate flower perianth (lodicules) absent; stamens absent; pistil 1; ovary superior, somewhat ovoid, ca. 1 × 0.7 mm, pale green, 1–chambered with 1 ovule; style 2–branched, basal portion within palea ± 5–sided, 3.5 mm long, translucent, the stigmatic branches nearly fully exserted at top of lower glume, spreading and variously curved or twisted, ca. 6 mm long, pale green.
Staminate spikelet oblanceoloid; glumes 2, lower glume oblanceolate, ca. 9 × 2.2—2.4 mm, having many fine veins, scabrous, somewhat keel–like, and with 2 lines of microhairs, not membranous, upper glume cupping flower, ovate, ca. 8.5 × 4 mm; lemma membranous, broadly triangular half–sheathing, 6—7 mm long, fleshy–membranous; palea oblanceolate, 4.5—6 × 2 mm, < lemma, fleshy–membranous.
Staminate flower perianth (lodicules) 2, fan–shaped, ca. 0.8 × 0.8 mm, translucent, fleshy and somewhat crescent–shaped in ×–section, minutely toothed or jagged on top margin; stamens 3, free; filaments within spikelet 1.8—2 mm long, when anthers released threadlike and ca. 6 mm long, white; anthers exserted and pendent to lower side of spike, dorsifixed, dithecal, 5.5—6 mm long, pale yellow in bud aging crimson to maroon, longitudinally dehiscent; pollen pale yellow; pistil absent.
Fruit achene (caryopsis) tightly enclosed in bracts of pistillate spikelet and dispersed attached at node to rame segment; achene ovoid, ca. 3.5 × 2.5 mm, whitish when dispersed.
A. C. Gibson