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The grass genera of the world

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

Setaria P. Beauv.

From the Latin seta (a bristle), alluding to bristly inflorescences.

Type species: Type: S. viridis (L.) P.Beauv.

Including Acrochaete Peter, Chaetochloa Scribn., Miliastrum Fabric., Tansaniochloa Rauschert

Excluding Camusiella, Cymbosetaria, Paspalidium

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 10–320 cm high; herbaceous; branched above (usually sparsely to amply), or unbranched above. The branching simple (usually), or fastigiate (e.g., S. surgens). Culm leaf sheaths keeled. Culm internodes solid, or hollow. Young shoots extravaginal, or intravaginal, or extravaginal and intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades broad, or narrow; usually not cordate, not sagittate (occasionally sagittate or hastate, then perhaps referable to Cymbosetaria); flat, or folded; without abaxial multicellular glands; pseudopetiolate (occasionally), or not pseudopetiolate; pinnately veined to palmately veined (rarely), or parallel veined; without cross venation; persistent; rolled in bud, or once-folded in bud, or folded like a fan in bud (in Sect. Ptychophyllum). Ligule present; a fringed membrane (narrow), or a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and male-only, or hermaphrodite and sterile (when clustered, often not all fully developed). Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous. Apomictic, or reproducing sexually. Viviparous (sometimes), or not viviparous.

Inflorescence. Inflorescence of spicate main branches (not uncommonly so - e.g., in Sect. Ptychophyllum - though this is ignored in many published keys), or a false spike, with spikelets on contracted axes, or paniculate (the primary branches arranged all the way round the main axis, by contrast with Paspalidium); open, or contracted; when contracted more or less ovoid, or spicate, or more or less irregular. Primary inflorescence branches inserted all around the main axis. Inflorescence axes not ending in spikelets (produced into ‘bristles’ beyond the spikelets). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets with ‘involucres’ of ‘bristles’, or subtended by solitary ‘bristles’ (e.g., in Sect. Ptychophyllum). The ‘bristles’ relatively slender, not spiny; persisting on the axis. Spikelets secund (when the spikelets are on clear primary branches, as in Sect. Ptychophyllum), or not secund; subsessile, or pedicellate. Pedicel apices discoid. Spikelets not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 2–4 mm long; elliptic, or ovate, or obovate; compressed dorsiventrally; falling with the glumes, or not disarticulating (in cultivated forms). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; very unequal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; awnless; membranous. Lower glume 3–6 nerved. Upper glume 3–9 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets fully developed to reduced; not becoming conspicuously hardened and enlarged laterally. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 5 nerved, or 7 nerved (rarely); more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; rugose; becoming indurated (crustaceous); yellow in fruit; entire; pointed; awnless (usually apiculate); hairless; usually non-carinate (but cymbiform in species perhaps referable to Cymbosetaria); having the margins inrolled against the palea; with a clear germination flap; 1–5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles basally fused, or free to their bases. Stigmas 2; white, or red pigmented.

Fruit, embryo and seedling. Fruit small; ellipsoid to subglobose; compressed dorsiventrally; sculptured, or smooth. Hilum short. Embryo large; waisted, or not waisted. 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; with a loose coleoptile. First seedling leaf with a well-developed lamina. The lamina broad; curved; veins ‘many’.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs (34–)38–96(–102) microns long. Microhair basal cells 21 microns long. Microhairs 7.5–8.4–9 microns wide at the septum. Microhair total length/width at septum 9.3–11.6. Microhair apical cells (16–)18–59(–62) microns long. Microhair apical cell/total length ratio (0.52–)0.57–0.64(–0.69). Stomata common; 39–42 microns long. Subsidiaries low to high dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; not paired (solitary); when present, silicified, or not silicified. Intercostal silica bodies present and perfectly developed (few); when present, cross-shaped, or vertically elongated-nodular. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired (rarely). Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; biochemical type NADP–ME (5 species); XyMS–. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (somtimes the epidermis largely, irregularly bulliform); commonly in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres (few cells).

Culm anatomy. Culm internode bundles scattered.

Phytochemistry. Leaves containing flavonoid sulphates (S. chevalieri), or without flavonoid sulphates (10 species).

Cytology. Chromosome base number, x = 9 and 10. 2n = 18, 36, 54, 63, and 72, or 36–54. 2, 4, 6, and 8 ploid. Chromosomes ‘small’. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. About 110 species.

Distribution, phytogeography, ecology. Tropical and warm temperate.

Commonly adventive. Generally mesophytic; shade species (e.g. S. palmifolia), or species of open habitats. In woodland, grassland, weedy places.

Economic aspects. Significant weed species: S. adhaerens, S. barbata, S. faberi, S. glauca, S. gracilis, S. italica, S. pallide-fusca, S. palmifolia, S. paniculifera, S. poiretiana, S. sphacelata, S. verticillata, S. verticilliformis, S. viridis. Cultivated fodder: S. sphacelata (Nandi). Important native pasture species: e.g. S. incrassata, S. kagarensis, S. longiseta, S. macrostachya, S. sphacelata. Grain crop species: S. italica (Foxtail Millet) - as a major (China) or minor cereal, and as birdseed. S. palmifolia sometimes cultivated as a vegetable.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia chaetochloae, Puccinia dolosa, Puccinia graminis, Puccinia substriata, ‘Uromycessetariae-italicae, and Puccinia esclavensis. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporium, and Ustilago.

References, etc. Morphological/taxonomic: Clayton 1979. Leaf anatomical: Metcalfe 1960; studied by us - S. geniculata (Lam.) Beauv., S. palmifolia (Koenig) Stapf, S. verticillata (L.) Beauv.

Illustrations. • S. dielsii: Gardner, 1952. • S. pallidifusca and S. verticillata: Fl. W. Trop. Afr. (1936). • S. parviflora, as imberbis: Wood, Natal Plants 2 (1904). • S. rigida: Wood, Natal Plants 2 (1904). • S. verticillata, general aspect: Eng. Bot. (1872). • General aspect (S. verticillata): Gibbs Russell et al., 1990. • S. viridis, general aspect: Eng. Bot. (1872). • Inflorescence with some spikelets shed (S. geniculata). • Inflorescence (part, close-up) of S. oplismenoides. • Inflorescence detail of S. palmifolia. • Detailing involucres of S. geniculata. Setaria geniculata. Involucres persistent (bristles continuous with the rachis). • Opened spikelet showing female-fertile floret (S. geniculata). • Floret, lemma (S. glaucescens). Setaria glaucescens. Glumes removed, to show rugose, indurated lemma back. • S. geniculata, abaxial epidermis of leaf blade: this project. • S. geniculata, abaxial epidermis of leaf blade: this project. • S. italica, T.S. midrib zone of leaf blade: this project. • S. italica, T.S. of leaf blade - electron micrograph: this project. Setaria italica. C4 type NADP-ME. • Pollen antigens: Watson and Knox (1976)

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.’.