Tropical Dropseed

Annual, delicate. Culms tufted, weak, 20–100 cm tall. Leaf sheaths glabrous; leaf blades linear, flat or folded, 5–20 × 0.2–0.5 cm, glabrous; ligule 0.2–0.3 mm. Panicle narrowly oblong, open, diffuse, 10–40 × 2–6 cm; lowest primary branches single or paired, branches capillary, lower 1/2 bare, secondary branches spreading. Spikelets gray or purplish, 0.8–1 mm, gaping at maturity; lower glume oblong, 0.1–0.4 mm, truncate-erose; upper glume ovate-oblong, 0.3–0.5 mm, subacute; lemma ovate, as long as spikelet, acute to obtuse. Anthers 3, 0.1–0.3 mm. Grain obovate. 0.4–0.7 mm, truncate. 2n = 12.

Disturbed or cultivated places at low elevations, introduced. S Taiwan [native to tropical America; now widely adventive in warm parts of the world].

Panicum tenuissimum Martius ex Schrank, Denkschr. Königl.-Baier. Bot. Ges. Regensburg 2: 26. 1822.

Sporobolus tenuissimus (Schrank) Kuntze, Rev. Gen. 3 2 : 369
1898.
Panicum tenuis simum Schrank, Denks. Bot. Ges. Regensb. 2: 26. 1822. Agrosticula muralis Raddi, Agrost. Bras. 33. 1823. (Type from Brazil.)
Sporobolus muralis Hitchc. & Chase, Contr. U. S. Nat. Herb. 18: 368. 1917. (Based on Agrosticula muralis Raddi.)
Annual; culms slender, erect, compressed, glabrous, 25-75 cm. tall; sheaths glabrous, compressed-keeled; ligule very short, ciliate; blades flat, thin, long-acuminate, glabrous or nearly so, 5-15 cm. long, the uppermost blades not much reduced, 1-3 mm. wide; panicles about half the length of the entire culm, narrow, open, 3-6 cm. wide, the branches and branchlets glabrous, capillary, spreading; spikelets glabrous, about 1 mm. long, on slender glabrous pedicels; first glume about one fourth, the second about half the length of the spikelet.
Type locality: Brazil.
Distribution: Waste ground, Virgin Islands through the Lesser Antilles to Brazil.

Annuals, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems caespitose, tufted, or clustered, Stems te rete, round in cross section, or polygonal, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Ligule present, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence simple spikes, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence branches more than 10 to numerous, Flowers bisexual, Spikelets pedicellate, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikelets solitary at rachis nodes , Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes 1 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma similar in texture to glumes, Lemma 1 nerved, Lemma glabrous, Lemma apex acute or acuminate, Lemma awnless, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea about equal to lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.