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The grass genera of the world

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

Chaetopoa C.E. Hubb.

Habit, vegetative morphology. Annual; loosely caespitose. Culms 15–60 cm high (slender, geniculate-ascending); herbaceous; branched above. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheath margins free. The sheaths with spreading to reflexed white hairs and tubercles. Leaf blades narrow; 2–6 mm wide (6.5–30 cm long); flat; without cross venation. Ligule an unfringed membrane; 4 mm long (lacerate above).

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, male-only, and sterile; homomorphic (the central fertile and outer sterile spikelets of the cluster superficially similar).

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (dense, narrow, of numerous glomerules each comprising six outer sterile involucral spikelets and a central fertile one); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to glomerules); disarticulating; falling entire (i.e., the glomerules falling - the main axis persistent). Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches (but with ‘false involucres’ of sterile spikelets); not secund; pedicellate (all short-pedicelled); consistently in ‘long-and-short’ combinations; unequally pedicellate in each combination (one of the sterile spikelets is longer-pedicelled than the rest, and has a longer G1). The ‘shorter’ spikelets hermaphrodite and sterile. The ‘longer’ spikelets sterile.

Female-sterile spikelets. The ‘involucral spikelets’ occasionally male, usually sterile; glumes both bristle-like (by contrast with the involucral G1 in Anthephora); lower floret reduced to a membranous lemma, L2 reduced or absent.

Female-fertile spikelets. Spikelets 4–5 mm long; slightly compressed dorsiventrally; falling with the glumes (i.e., with the glomerules). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; more or less equal; about equalling the spikelets to exceeding the spikelets; glumes as long as or longer than the florets; subulate; similar (both more or less bristle-like, the G2 somewhat broader below). Lower glume 1 nerved. Upper glume 2 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. Palea of the proximal incomplete florets reduced. The proximal incomplete florets sterile. The proximal lemmas awnless (but apically acuminate and mucronate); 7–9 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (chartaceous to membranous); not becoming indurated.

Female-fertile florets 1. Lemmas narrowly elliptical, acute; not becoming indurated; entire; pointed; mucronate; hairless; non-carinate (convex); having the margins lying flat on the palea; 3–5 nerved. Palea present; relatively long, or conspicuous but relatively short; entire (obtuse, ovate); awnless, without apical setae; not indurated (hyaline); 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically hairy. Styles fused. Stigmas 2; white.

Fruit, embryo and seedling. Fruit small (about 1.5 mm long); compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrowly rectangular); of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells (these rather irregular in shape). Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present (and fairly common alongside the veins, but hard to find); elongated; clearly two-celled; panicoid-type; 51–55.8–60 microns long; 5.4–6–7.5 microns wide at the septum. Microhair total length/width at septum 6.8–9.4–10.6. Microhair apical cells 30–33–36 microns long. Microhair apical cell/total length ratio 0.53–0.59–0.63. Stomata common; 27–30 microns long. Subsidiaries low to high dome-shaped, or triangular. Guard-cells overlapped by the interstomatals (slightly, in places), or overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (excluding the short cells associated with the bases of macrohairs). Macrohairs and prickles abundant. Costal short-cells conspicuously in long rows (the rows often interrupted by prickles), or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies absent to poorly developed; probably ‘panicoid-type’ (but the silica bodies themselves obscure in the material seen); cross shaped, or dumb-bell shaped (?).

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines even. Leaf blade ‘nodular’ in section (the abaxial ribs rather more prominent); with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles (the large, median keel bundle flanked on either side by 2–3 smaller bundles); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms not present in discrete, regular adaxial groups (the epidermis extensively bulliform). 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 (cf. Anthephora). Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Anthephorinae. 2 species.

Distribution, phytogeography, ecology. Tanzania.

Species of open habitats. Soil pockets on rocks.

References, etc. Morphological/taxonomic: Hubbard 1967; Clayton 1977. Leaf anatomical: this project.


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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: 13th November 2017. delta-intkey.com/grass’.

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