26.08   SORGHUM Moench
Mary E. Barkworth

Plants annual or perennial. Culms 50-500+ cm; internodes solid. Leaves not aromatic, basal and cauline; auricles absent; ligules membranous and ciliate or of hairs; blades usually flat. Inflorescences terminal, panicles with evident rachises; primary branches whorled, compound, the ultimate units rames; rames with most spikelets in heterogamous sessile-pedicellate spikelet pairs, terminal spikelet unit on each rame usually a triplet of 1 sessile and 2 pedicellate spikelets, rame axes without a translucent median line; disarticulation in the rames below the sessile spikelets, sometimes also below the pedicellate spikelets (cultivated taxa not or only tardily disarticulating). Sessile spikelets dorsally compressed, calluses blunt or pointed; lower glumes dorsally compressed and rounded basally, 2-keeled or winged distally, 5-15-veined, usually unawned; upper glumes 2-keeled, sometimes awned; lower florets reduced to hyaline lemmas; upper florets pistillate or bisexual, lemmas hyaline, sometimes awned. Pedicels slender, neither appressed nor fused to the rame axes. Pedicellate spikelets staminate or sterile, well-developed, often subequal to the sessile spikelets in size. x = 10. Name from the Italian word for the plant, sorgho.

Most of the approximately 25 species of Sorghum are native to tropical and subtropical regions of the Eastern Hemisphere, but one is native to Mexico. Two have been introduced into the Flora region. Some species are grown as forage, although they produce cyanogenic compounds. Sorghum bicolor is widely cultivated, being used as a grain, for syrup, and as a flavoring for beer.

Spangler (2000) found, using ndhF data, that Sorghum is polyphyletic, forming two distinct clades. The two species treated here were in the same clade. He found Microstegium and Miscanthus to be more closely related to Sorghum than Sorghastrum.

SELECTED REFERENCES Clayton, W.D. and S.A Renvoize. 1982. Flora of Tropical East Africa. Gramineae (Part 3). A.A. Balkema, Rotterdam, The Netherlands. 448 pp.; de Wet, J.M.J. 1978. Systematics and evolution of Sorghum sect. Sorghum (Gramineae). Amer. J. Bot. 65:477-484; Dillon, S.L., P.K. Lawrence, and R.J. Henry. 2001. The use of ribosomal ITS to determine phylogenetic relationships within Sorghum. Pl. Syst. Evol. 230:97-110; Harlan, J.R. and J.M.J. de Wet. 1972. Sources of variation in Cynodon dactylon (L.) Pers. Crop Sci. 12:172-176; Harlan, J.R., J.M.J. de Wet, and A.B.L. Stemler (eds.). 1976. Origins of African Plant Domestication. Mouton Press, The Hague, The Netherlands. 498 pp.; Spangler, R.E. 2000. Andropogoneae systematics and generic limits in Sorghum. Pp. 167-170 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. International Symposium on Grass Systematics and Evolution (3rd:1998). CSIRO Publishing, Collingwood, Victoria, Australia. 408 pp.
Plants perennial, rhizomatous; spikelets disarticulating at maturity; caryopses not exposed at maturity ..... 1. S. halepense
Plants usually annual, sometimes short-lived perennials; spikelets either not disarticulating or doing so tardily; caryopses often exposed at maturity ..... 2. S. bicolor

1.   Sorghum halepense (L.) Pers.
Johnson Grass

Plants perennial; rhizomatous. Culms 50-200 cm tall, 0.4-2 cm thick; nodes appressed pubescent; internodes glabrous. Ligules 2-6 mm, membranous, conspicuously ciliate; blades 10-90 cm long, 8-40 mm wide. Panicles 10-50 cm long, 5-25 cm wide, primary branches compound, terminating in rames of 1-5 spikelet pairs; disarticulation usually beneath the sessile spikelets, sometimes also beneath the pedicellate spikelets. Sessile spikelets bisexual, 3.8-6.5 mm long, 1.5-2.3 mm wide; calluses blunt; glumes indurate, shiny, appressed pubescent; upper lemmas unawned, or with a geniculate, twisted awn to 13 mm; anthers 1.9-2.7 mm. Pedicels 1.8-3.3 mm. Pedicellate spikelets staminate, 3.6-5.6 mm; glumes membranous to coriaceous, unawned. Caryopses not exposed at maturity. 2n = 20, 40; several dysploid counts also reported.

Sorghum halepense is native to the Mediterranean region. It is sometimes grown for forage in North America, but it is considered a serious weed in warmer parts of the United States. It hybridizes readily with S. bicolor, and derivatives of such hybrids are widespread. The annual Sorghum almum Parodi, which has wider (2-2.8 mm) sessile spikelets with more veins in the lower glumes (13-15 versus 10-13) than S. halepense, is one such derivative.

2.   Sorghum bicolor (L.) Moench

Plants annual or short-lived perennials; often tillering, without rhizomes. Culms 50-500+ cm tall, 1-5 cm thick, sometimes branching above the base; nodes glabrous or appressed pubescent; internodes glabrous. Ligules 1-4 mm; blades 5-100 cm long, 5-100 mm wide, sometimes glabrous. Panicles 5-60 cm long, 3-30 cm wide, open or contracted, primary branches compound, terminating in rames with 2-7 spikelet pairs; disarticulation usually not occurring or tardy. Sessile spikelets bisexual, 3-9 mm, lanceolate to ovate; calluses blunt; glumes coriaceous to membranous, glabrous, densely hirsute, or pubescent, keels usually winged; upper lemmas unawned or with a geniculate, twisted, 5-30 mm awn; anthers 2-2.8 mm. Pedicels 1-2.6 mm. Pedicellate spikelets 3-6 mm, usually shorter than the sessile spikelets, staminate or sterile. Caryopses often exposed at maturity. 2n = 20, 40.

Sorghum bicolor was domesticated in Africa 3000 years ago, reached northwestern India before 2500 B.C., and became an important crop in China after the Mongolian conquest. It was introduced to the Western Hemisphere in the early sixteenth century, and is now an important crop in the United States and Mexico. Numerous cultivated strains exist, some of which have been formally named. They are all interfertile with each other and with other wild species of Sorghum.

The treatment presented here is based on de Wet (1978) and is somewhat artificial. Sorghum bicolor subsp. arundinaceum is the wild progenitor of the cultivated strains, all of which are treated as S. bicolor subsp. bicolor. These strains tend to lose their distinguishing characteristics if left to themselves. They will also hybridize with subsp. arundinaceum, and these hybrids can backcross to either parent, resulting in plants that may strongly resemble one parent while having some characteristics of the other. All such hybrids and backcrosses are treated here as S. bicolor subsp. drummondii.

Inflorescences branches remaining intact at maturity; caryopses exposed at maturity; sessile spikelets 3-9 mm long, elliptic to oblong ..... subsp. bicolor
Inflorescences branches rames, disarticulating at maturity, sometimes tardily; caryopses not exposed at maturity; sessile spikelets 5-8 mm long, lanceolate to elliptic (2)
Rames readily disarticulating ..... subsp. arundinaceum
Rames disarticulating tardily ..... subsp. drummondii

Sorghum bicolor subsp. arundinaceum (Desv.) de Wet & J.R. Harlan

Plants annual or weakly biennial. Culms to 4 m, slender to stout. Rames readily disarticulating at maturity, with 1-5 nodes. Sessile spikelets 5-8 mm, lanceolate to elliptic. Caryopses not exposed at maturity.

Sorghum bicolor subsp. arundinaceum is native to, and most common, in Africa, but some strains have been introduced into the Western Hemisphere.

Sorghum bicolor (L.) Moench subsp. bicolor
Sorghum, Broomcorn, Sorgo

Plants annual. Culms to 5 m or more, stout, frequently tillering. Inflorescence branches remaining intact at maturity, with 1-5 nodes. Sessile spikelets 3-9 mm long, 2-5 mm wide, elliptic to oblong. Caryopses exposed at maturity.

All the cultivated sorghums are placed in Sorghum bicolor subsp. bicolor. Grain sorghums have short panicles and panicle branches, broomcorns have elongate panicles and panicle branches, and sweet sorghums or sorgho produce an abundance of sweet juice in their stems. For a more detailed treatment, see Harlan and de Wet (1972).

Sorghum bicolor subsp. drummondii (Steud.) de Wet
Chicken Corn, Sudangrass

Plants annual. Culms to 4 m, relatively stout. Rames usually tardily disarticulating, mostly with 3-5 nodes. Sessile spikelets 5-6 mm, lanceolate to elliptic. Caryopses not exposed at maturity.

The hybrids treated here as Sorghum bicolor subsp. drummondii are most common in the Eastern Hemisphere, but a few are cultivated in the United States. Among these are the plants known as 'chicken corn' and 'Sudangrass' [= S. sudanense (Piper) Stapf] (de Wet 1978).