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The grass genera of the world

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

Stereochlaena Hackel

Including Chloridion Stapf

Excluding Baptorhachis

Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms 60–150 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear to linear-lanceolate; narrow; 2–8(–11) mm wide; flat; without cross venation; persistent. Ligule present; a fringed membrane; 0.2–0.7 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches (slender spike-like racemes); paired or digitate. Primary inflorescence branches 2–8. Rachides winged (with narrow, fringed wings). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’. The racemes spikelet bearing to the base, or without spikelets towards the base. Spikelet-bearing axes persistent. Spikelets paired; secund; biseriate; shortly pedicellate, or subsessile; consistently in ‘long-and-short’ combinations (but homogamous). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite.

Female-fertile spikelets. Spikelets 2–4.5 mm long; abaxial; compressed dorsiventrally; flattened dorsally and ventrally; falling with the glumes; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes one per spikelet, or two; minute, or relatively large (the G1 minute or absent, the G2 minute to almost as long as the spikelet); when both present, very unequal; (the upper) shorter than the spikelets to about equalling the spikelets; shorter than the adjacent lemmas to long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; without conspicuous tufts or rows of hairs; awned (G2 only, sometimes), or awnless; non-carinate; when both present, very dissimilar. Lower glume when present, 0 nerved. Upper glume 1–3 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, reduced. The proximal incomplete florets sterile. The proximal lemmas awned (the terminal awn from 3–30 mm long); 5 nerved, or 7 nerved (in S. tridentata, the lateral keels form a tooth on either side of the awn); more or less equalling the female-fertile lemmas (excluding the awn); less firm than the female-fertile lemmas (membranous, scabrid, 2-keeled or not); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (papery); not becoming indurated; brown in fruit; entire; pointed; awnless (sometimes apiculate); hairless; having the margins lying flat on the palea; with a clear germination flap; faintly 3 nerved. Palea present; relatively long; 2-nerved. Lodicules absent. Stamens 3. Anthers about 2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small (about 1.7 mm long); elongate ellipsoid; compressed dorsiventrally. Hilum short (punctiform). Embryo large (about 1/3 the fruit length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones with typical long-cells and exhibiting many atypical long-cells (varying from place to place). Mid-intercostal long-cells rectangular (elongated to almost square); having markedly sinuous walls. Microhairs present; panicoid-type; 78–84 microns long; 4.5–6 microns wide at the septum. Microhair total length/width at septum 13–18.7. Microhair apical cells 51–52.5 microns long. Microhair apical cell/total length ratio 0.61–0.67. Stomata common; 30–32(–33) microns long. Subsidiaries parallel-sided (in some parts of the blade), or dome-shaped, or triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (the apparent examples being prickle bases). Sometimes exhibiting macrohairs with complex cushion bases. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; nearly all cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (apparently, in places). Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (one large and up to 8 small bundles); with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (bulliform cells constituting most of the epidermis). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 5 species.

Distribution, phytogeography, ecology. Tropical east Africa.

Mesophytic; species of open habitats; glycophytic. Savanna grasslands.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia stenotaphri. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Morphological/taxonomic: Stapf 1900b; Clayton 1978b. Leaf anatomical: studied by us - S. cameronii (Stapf) Pilger.

Illustrations. • S.cameronii, as Chloridion: Hook. Ic. Pl. 27 (1901). • General aspect (S. cameronii): Gibbs Russell et al., 1990. • S. cameronii, abaxial epidermis of leaf blade: this project. • TS leaf blade of S. cameronii: this project

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.’.