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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Sorghum Moench

From sorgho, the Italian name for the plant.

Including Blumenbachia Koel., Sarga Ewart & White, Vacoparis

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 60–300 cm high; herbaceous; sparsely branched above (rarely), or unbranched above. The branching simple. Culm nodes hairy (e.g. in subgenera Parasorghum and Stiposorghum), or glabrous. Culm internodes solid (or sometimes hollow below). Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; not cordate, not sagittate; not setaceous; usually flat; without cross venation; persistent; rolled in bud. Ligule present; an unfringed membrane to a fringed membrane, or a fringe of hairs (rarely). Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic; all in heterogamous combinations. Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence paniculate, or of spicate main branches (usually large, the branched or simple primary branches usually whorled); open, or contracted; with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced, or ‘racemes’ (short racemes with 1–6(-8) articles only); the spikelet-bearing axes with only one spikelet-bearing ‘article’, or with 2–3 spikelet-bearing ‘articles’, or with 4–5 spikelet-bearing ‘articles’, or with 6–10 spikelet-bearing ‘articles’ (rarely); with very slender rachides; disarticulating, or persistent (in cultivated forms); falling entire (when reduced to one joint), or disarticulating at the joints. ‘Articles’ linear (flattened); without a basal callus-knob; disarticulating transversely. Spikelets paired, or in triplets (terminal); not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile (but not reduced to the pedicel, by contrast with Sorghastrum).

Female-sterile spikelets. The pedicellate spikelet male or sterile, much narrower and awnless or reduced to a glume, very rarely suppressed (S. angustum.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes, or not disarticulating (in cultivated forms). Rachilla terminated by a female-fertile floret. Hairy callus present, or absent. Callus pointed, or blunt.

Glumes two; more or less equal; long relative to the adjacent lemmas; without conspicuous tufts or rows of hairs; awnless, or awned (the upper, sometimes); very dissimilar (the lower flat or rounded on the back save at the summit, upper naviculate). Lower glume not two-keeled (below, but becoming two-keeled and winged above); convex on the back to flattened on the back; not pitted; relatively smooth; 5–11 nerved. Upper glume 3–11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved; similar in texture to the female-fertile lemmas (hyaline, ciliate); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline, ciliate); not becoming indurated; incised; awnless to mucronate (rarely), or awned. Awns when present, 1; from a sinus; geniculate; hairless (glabrous); much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; non-carinate; 1–3 nerved. Palea present, or absent; when present, relatively long, or conspicuous but relatively short, or very reduced; not indurated (hyaline); nerveless, or 2-nerved. Lodicules present; 2; free; more or less fleshy; usually ciliate. Stamens 3. Anthers penicillate, or not penicillate. Ovary apically glabrous, or apically hairy (occasionally with a terminal hair tuft, e.g. S. intrans). Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small, or medium sized, or large; compressed dorsiventrally, or not noticeably compressed. Hilum short. Embryo large. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–30 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent. Intercostal papillae over-arching the stomata; several per cell (the costal papillae consisting of fingerlike projections, the intercostal ones of larger, oblique swellings). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 34–78 microns long; 6.6–9.6 microns wide at the septum. Microhair total length/width at septum 6.3–11.8. Microhair apical cells (15–)21–30(–36) microns long. Microhair apical cell/total length ratio 0.39–0.62. Stomata common; 27–36 microns long. Subsidiaries usually at least somewhat triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (rare); when present, in cork/silica-cell pairs, or not paired (solitary); silicified. Intercostal silica bodies when present, tall-and-narrow, or crescentic. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; usually cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (3 species); XyMS–. PCR sheath outlines uneven. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (often irregularly grouped and/or occupying most of the epidermis); sometimes in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles scattered.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (4 species).

Special diagnostic feature. Spikelets paired, all the pedicels spikelet-bearing.

Cytology. Chromosome base number, x = 5. 2n = 10, 20, and 40 (and aneuploids - 26, 33, 38–39 etc.). Chromosomes ‘small’. Haploid nuclear DNA content 1.2–2.7 pg (8 4x species, mean 2.3). Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Sorghinae. About 30 species.

Distribution, phytogeography, ecology. Tropical and subtropical.

Commonly adventive. Mesophytic; shade species, or species of open habitats; glycophytic. Savanna and forest margins, alluvial plains and disturbed ground.

Economic aspects. Significant weed species: S. almum, S. bicolor, S. halepense. Cultivated fodder: S. halepense (Johnson), and hybrids involving S. arundinaceum, S. bicolor and S. halepense (e.g. Sudan). Grain crop species: S. bicolor (Sorghum), with many cultivars.

Hybrids. Intergeneric hybrids with Saccharum.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia nakanishikii and Puccinia levis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - S. halepense (L.) Pers., S. leiocladum (Hackel) Hubbard.

Illustrations. • S. bicolor, as Andropogon sorghum var. usorum: Wood, Natal Plants 2 (1904). • S. plumosum: Gardner, 1952. • General aspect (S. halepense): Gibbs Russell et al., 1990. • S. leiocladum, abaxial epidermis of leaf blade: this project. • Pollen antigens: Watson and Knox (1976). • Pollen antigens: cross-reactions against anti-Lolium serum. • Pollen antigens: cross-reactions against anti-Lolium serum. • Heat stable pollen antigens (allergens): cross-reactions against anti-Lolium serum. • Pollen antigens: cross-reactions against anti-Cynodon serum. • Pollen antigens: cross-reactions against anti-Zea serum. • Pollen antigens: cross-reactions against anti-Zea serum

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.