John W. Thieret†

Plants annual or perennial; straggling. Culms to 100 cm, often decumbent. Leaves not aromatic; ligules membranous; blades narrowly-elliptic to lanceolate, often pseudopetiolate. Inflorescences terminal, subdigitate to racemose clusters of 1-few rames; rame internodes slender, without a translucent longitudinal groove; disarticulation in the rames beneath the sessile spikelets, and below the pedicellate spikelets. Spikelets in homogamous, homomorphic, sessile-pedicellate pairs, with 1 or 2 florets. Lower glumes herbaceous to cartilaginous, longitudinally grooved, margins inflexed, 4-6-veined, usually keeled; upper glumes 3-veined, mucronate or shortly awned; lower florets absent, or reduced and sterile; upper florets bisexual; upper lemmas usually awned; anthers (2)3. x = 10. Pedicels not fused to the rame axes. Name from the Greek micros, small, and stege, cover, possibly alluding to small glumes.

Microstegium is a genus of approximately 15 species, most of which are native to southeastern Asia; one is established in the Flora region.

SELECTED REFERENCES Fairbrothers, D.E. and J.R. Gray. 1972. Microstegium vimineum (Trin.) A. Camus (Gramineae) in the United States. Bull. Torrey Bot. Club 99:97-100; Hunt, D.M. and R.E. Zaremba. 1992. The northeastward spread of Microstegium vimineum (Poaceae) into New York and adjacent states. Rhodora 94:167-170; Mehrhoff, L.J. 2000. Perennial Microstegium vimineum (Poaceae): An apparent misidentification. J. Torrey Bot. Soc. 127:251-254.

1.   Microstegium vimineum (Trin.) A. Camus
Nepalese Browntop

Plants annual. Culms 40-100 cm tall, 1-1.5 mm thick, freely branching, lower portions prostrate, rooting at the nodes, terminal portions and flowering branches erect; nodes glabrous. Sheaths shorter than the internodes, mostly glabrous or sparsely pubescent above, margins ciliate, becoming pilose at the throat; ligules 0.5-0.8 mm, truncate; blades 3-10 cm long, 8-15 mm wide, glabrous or sparsely pubescent, bases cuneate, midveins white, apices attenuate, acute. Cleistogamous inflorescences concealed in the upper sheaths; chasmogamous inflorescence exserted, of (1)2-4(6) racemose to subdigitate, erect to ascending rames; rames 3-7 cm, glaucous-green; internodes 3.5-5 mm, gradually widened above, ciliate. Spikelets 3.7-6.5 mm. Lower glumes2-keeled, subtruncate to shallowly 2-toothed; upper glumes acute; upper lemmas usually awned, awns 2-5(15) mm, often concealed by the glumes; anthers 3, 0.7-1 mm. Pedicels 3-4 mm. 2n = 40.

Microstegium vimineum was introduced to Tennessee from Asia around 1919 and is now established in much of the eastern United States. Although often associated with forested and wetland areas, it also does well in many disturbed areas. In suitable habitats it quickly spreads by rooting from its prostrate culms, forming dense, monospecific stands. It is sometimes confused with Leersia viriginica, but differs from that species in its glabrous cauline nodes and the presence of hairs at the summit of the leaf sheaths. In addition, M. vimineum flowers in late September and October and is clearly a member of the Andropogoneae, whereas L. viriginica flowers in June through July and is a member of the Oryzeae.