The grass genera of the world
Type species: Type: S. glabrum Trin. = S. secundatum (Walt.) Kuntze, p.p.
Including Diastemenanthe Steud., Ophiurinella Desv.
Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose. Culms 10–60 cm high; herbaceous; branched above. Culm nodes glabrous. Culm leaf sheaths compressed, or rounded. Leaves not basally aggregated; non-auriculate. The sheaths compressed. Leaf blades lanceolate to elliptic; broad, or narrow; flat, or folded (when young); pseudopetiolate, or not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent (rarely); once-folded in bud. Ligule present; a fringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.
Inflorescence. Inflorescence of spicate main branches, or a false spike, with spikelets on contracted axes (the spikelets 1 to several, in very short spike-like racemes embedded in hollows of the corky or foliaceous common axis, or in longer racemes closely appressed to it); non-digitate. Primary inflorescence branches borne biseriately on one side of the main axis, or borne distichously. Inflorescence axes not ending in spikelets (minutely bare-tipped, when not coalesced with the main axis). Rachides hollowed. Inflorescence spatheate (the small racemes subtended/enclosed by spathes which are laterally adnate to the rachis), or espatheate; a complex of partial inflorescences and intervening foliar organs, or not comprising partial inflorescences and foliar organs. Spikelet-bearing axes very much reduced (sometimes reduced to one spikelet with no rachis extension, or coalesced with the main axis); disarticulating; falling entire (the free racemes falling with the joint of the main axis), or disarticulating at the joints (when the spikelet bearing unit consists of a coalesced main axis and branches). Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; secund.
Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; very unequal; (the longer) long relative to the adjacent lemmas, or shorter than the adjacent lemmas; dorsiventral to the rachis; awnless; very dissimilar (lower minute, scale-like, upper large, substantial), or similar (both small, scale-like). Lower glume 0 nerved. Upper glume 5–9 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 when present, fully developed. The proximal incomplete florets male, or sterile (rarely). The proximal lemmas awnless; 3 nerved, or 7–9 nerved; similar in texture to the female-fertile lemmas, or decidedly firmer than the female-fertile lemmas (leathery or papery); not becoming indurated.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (papery to subleathery); smooth to striate; not becoming indurated; yellow in fruit; entire; pointed; awnless; hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3–5 nerved. Palea present; relatively long; entire (pointed); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; fleshy. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles fused. Stigmas 2; white, or red pigmented.
Fruit, embryo and seedling. Disseminule comprising the rachis segment and associated structures, or consisting of the disarticulated spikelet-bearing inflorescence unit, or constituted by the complete, deciduous inflorescence. Fruit small; ellipsoid; compressed dorsiventrally. Hilum short. Embryo large; not waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. 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; (45–)54–78(–84) microns long; 9–12(–13.5) microns wide at the septum. Microhair total length/width at septum 6.2–7.7. Microhair apical cells 32–62 microns long. Microhair apical cell/total length ratio 0.61–0.76. Stomata common; (27–)28.5–30(–33) microns long. Subsidiaries low dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (solitary); silicified, or not silicified. Intercostal silica bodies when present, tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped to dumb-bell shaped, or nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; without colourless mesophyll adaxially (but with colourless cells abaxially instead, here and sometimes with other main bundles). Bulliforms not present in discrete, regular adaxial groups (absent or irregularly disposed, apart from a group over the midrib). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 9. 2n = 18, 20, and 36. 2 and 4 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 7 species.
Distribution, phytogeography, ecology. Tropical and subtropical.
Commonly adventive. Mesophytic; species of open habitats; halophytic, or glycophytic. Usually in sandy soils near the coast, sometimes inland.
Economic aspects. Significant weed species: S. dimidiatum, S. secundatum. Important native pasture species: S. dimidiatum, S. secundatum. Lawns and/or playing fields: S. secundatum (in warm coastal regions).
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia stenotaphri and Uromyces setariae-italicae. Smuts from Ustilaginaceae. Ustilaginaceae Sorosporium, Sphacelotheca, and Ustilago.
References, etc. Morphological/taxonomic: Saur 1972. Leaf anatomical: Metcalfe 1960; studied by us - S. micranthum (Desv.) C.E. Hubb., S. secundatum (Walter) Kuntze.
Illustrations. • S. dimidiatum, as S. madagascariense: Kunth (1835). • S. secundatum: Gardner, 1952. • Inflorescence detail (S. secundatum). • S. micranthum, abaxial epidermis of leaf blade: this project. • S. secundatum, abaxial epidermis of leaf blade: this project. • 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. delta-intkey.com/grass’.