26.09   SORGHASTRUM Nash

Patricia Dávila Aranda
Stephan L. Hatch

Plants annual or perennial; cespitose, sometimes rhizomatous. Culms 50-300+ cm, erect, nodding or clambering, unbranched; nodes densely pubescent, particularly in young plants. Leaves not aromatic; ligules membranous, glabrous or pubescent; blades flat, involute, or folded. Inflorescences terminal, secund or equilateral panicles with evident rachises and numerous branches, not subtended by modified leaves; branches capillary, rebranching, with many rames, not subtended by modified leaves; disarticulation in the rames, beneath the sessile spikelets. Spikelets sessile, subtending a hairy pedicel (2 pedicels in the terminal spikelet units), dorsally compressed. Calluses blunt or sharp; glumes coriaceous; lower glumes pubescent, 5-9-veined, acute; upper glumes slightly longer, usually glabrous, 5-veined, truncate; lower florets reduced to hyaline lemmas; upper florets bisexual, lemmas hyaline, bifid, awned from the sinuses; awns usually once- or twice-geniculate, often spirally twisted, shortly strigose, brownish; anthers 3; ovaries glabrous. Caryopses flattened. Pedicels 3-6.5 mm, slender, not fused to the rame axes; pedicellate spikelets absent. x = 10. Name from Sorghum and the Latin suffix astrum, a poor imitation of, alluding to its similarity to Sorghum.

Sorghastrum includes about 18 species. Most are native to tropical or subtropical America, two are African, and four are native to the Flora region. Absence of the pedicellate spikelet, while confusing at first, makes Sorghastrum a readily recognizable genus. Its species range from sea level to approximately 3000 m, and can be found in a wide range of habitats. Two species, neither of which occur in the Flora region, are considered good forage.


SELECTED REFERENCES Dávila, P.D. 1988. Systematic revision of the genus Sorghastrum (Poaceae: Andropogoneae). Ph.D. dissertation, Iowa State University, Ames, Iowa, U.S.A. 333 pp.; Hall, D.W. 1982. Sorghastrum (Poaceae) in Florida. Sida 9:302-308; Sorrie, B.A. and S.W. Leonard. 1999. Noteworthy records of Mississippi vascular plants. Sida 18:889-908.

1
Awns 10-22(30) mm long, once-geniculate; plants rhizomatous ..... 3. S. nutans
Awns 21-40 mm long, twice-geniculate; plants not rhizomatous (2)
2
Pedicels sharply curved to recurved; panicles secund; sessile spikelets 0.8-1.2 mm wide..... 2. S. secundum
Pedicels flexuous; panicles not secund; sessile spikelets 1.1-1.8 mm wide..... 1. S. elliottii


1.   Sorghastrum elliottii (C. Mohr) Nash
Slender Indiangrass

Plants not rhizomatous. Culms 70-190 cm tall, 1.2-2.4 mm thick; internodes glabrous. Sheaths mostly glabrous, throats pubescent; ligules 2-5 mm, decurrent, ciliate; blades 20-55 cm long, 2.5-5.5(8) mm wide, mostly glabrous. Panicles 10-35 cm, open, straight to arching, dark purple; rachises 0.3-0.8 mm thick 1-2 mm above the lowest node, sometimes with a ring of hairs; branches capillary, flexuous, longest branches 19.5-34.5 cm. Spikelets 6-7.5 mm long, 1.1-1.4 mm wide, dark chestnut brown at maturity. Calluses 1-1.3 mm, blunt; lower glumes 5.5-7.3 mm, glabrous, 5-veined; upper glumes 6.2-7.5 mm; awns 25-40 mm, 5 times longer than the spikelets, twice-geniculate; anthers 2-3 mm. Caryopses 2-2.5 mm. Pedicels 3-6.5 mm, flexuous. 2n = 20.

Sorghastrum elliottii usually grows in dry, open woods on sandy terraces of the lowlands in the southeastern United States, often over a clay subsoil. Plants with straight panicles and sessile spikelets that are 1.3-1.8 mm wide are sometimes called S. apalachicolense D.W. Hall, but the variation appears to be continuous and such plants are included here in S. elliottii.


2.   Sorghastrum secundum (Elliott) Nash
Lopsided Indiangrass

Plants not rhizomatous. Culms 90-180 cm tall, 1.5-3 mm wide; internodes glabrous or pubescent beneath the nodes. Sheaths usually glabrous, occasionally pubescent in young plants; ligules 2.5-4(5.7) mm; blades 20-50 cm long, (1.8)3-6 mm wide, scabrous, particularly on the adaxial surfaces. Panicles 15-40 cm, straight to slightly arching, secund, somewhat open; nodes glabrous or almost so; branches erect or nearly so. Spikelets 6-8 mm long, 0.8-1.2 mm wide, lanceolate, dark brown to golden brown at maturity. Calluses 1-1.2 mm, blunt, densely bearded; lower glumes 6-7.5 mm, pubescent, truncate, 7-9-veined; upper glumes 6.5-8 mm, glabrous, acuminate, 5-veined; awns 30-40 mm, 4-5 times longer than the spikelets, twice-geniculate, dark brown; anthers 2.5-4.5 mm. Caryopses 2-3 mm. Pedicels 4-7.5 mm, pubescent, sharply curved to recurved. 2n = 20.

Sorghastrum secundum grows in woodlands, sandy soils, and occasionally at the edges of marshes, at elevations below 1000 m. Its native range extends north and west from Florida to the Appalachian Mountains; other records probably reflect introductions. The mountains may have effectively prevented its further spread to the northwest.

Sorghastrum secundum may be confused with plants of S. elliottii that are not at anthesis because both species may have straight to slightly arching panicles with ascending branches. They sometimes differ with respect to their rachis nodes, those of S. secundum being glabrous or almost glabrous whereas those of S. elliottii often have a ring of hairs.


3.   Sorghastrum nutans (L.) Nash
Indiangrass, Faux-Sorgho Penché

Plants rhizomatous, rhizomes short, stout, scaly. Culms 50-240 cm tall, 1.5-4.5 mm thick, erect; internodes glabrous. Sheaths glabrous or sparsely hispid; ligules 2-6 mm, usually with thick, pointed auricles; blades 10-70 cm long, 1-4 mm wide, usually glabrous. Panicles 20-75 cm, loosely contracted, yellowish to brownish; branches often flexible. Spikelets 5-8.7 mm. Calluses blunt, villous; lower glumes 5-8 mm, pubescent, 7-9-veined; upper glumes 5-8 mm, 5-veined; awns 10-22(30) mm, about 2-3 times longer than the spikelets, once-geniculate; anthers (2)3-5 mm. Caryopses 2-3 mm. Pedicels 3-6 mm, flexible. 2n = 20, 40, 80.

Sorghastrum nutans grows in a wide range of habitats, from prairies to woodlands, savannahs, and scrubland vegetation. It is native from Canada to Mexico, and was one of the four principal grasses of the tallgrass prairie that occupied the central United States prior to agricultural development of the region. It is frequently used for forage, for erosion control on slopes and along highways, and in restoration work. It is an attractive plant and can be used to advantage in flower arrangements. It grows readily from seed if adequate moisture is available. There are several cultivars on the market.