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The grass genera of the world

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

Apochiton C.E. Hubb.

Habit, vegetative morphology. Annual; caespitose (loosely), or decumbent. Culms 30–70 cm high; herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear; narrow; to 4 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane (but the fringe of short cilia); truncate; 0.5 mm long. Contra-ligule absent.

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

Inflorescence. Inflorescence paniculate; open (to 20 cm long); without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 6–8 mm long; oblong, or lanceolate; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; rachilla sparsely hairy; the rachilla extension with incomplete florets. Hairy callus present. The callus hairs white. Callus blunt.

Glumes present; two; very unequal to more or less equal; shorter than the adjacent lemmas; hairless; pointed (tapered into short points); awned (shortly), or awnless (then mucronate); carinate; similar (greyish, membranous, glabrous). Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped.

Female-fertile florets 3–5. Lemmas similar in texture to the glumes (membranous); smooth; not becoming indurated; entire; awned. Awns 1; median; apical (attenuate from the lemma); non-geniculate; hairless (scabrid); much shorter than the body of the lemma to about as long as the body of the lemma (2–3 mm); entered by one vein; persistent. Lemmas hairy (with white hairs over the lower two thirds); somewhat carinate; without a germination flap; 3 nerved. Palea present; relatively long (but shorter than the lemma); deeply bifid; awned (the two lobes attenuate into terminal awns about 2 mm long); not indurated (membranous); 2-nerved; 2-keeled. Palea keels hairy (with white hairs). Lodicules present; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers 1 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 2 mm long); ellipsoid; trigonous. Hilum short. Pericarp free. Embryo small (obscure).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell (large but rather inconspicuous, at one end of many of the long-cells). Long-cells similar in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (22.5–)24–27(–30) microns long. Microhair basal cells 10–11 microns long. Microhairs 9–12 microns wide at the septum. Microhair total length/width at septum 1.9–3.3. Microhair apical cells 9–12 microns long. Microhair apical cell/total length ratio 0.35–0.5. Stomata common; 30–33 microns long. Subsidiaries mostly low dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows (but the ‘short-cells’ tending to be rather long). Costal silica bodies confined to the central file(s) of the costal zones; ‘panicoid-type’ (mostly), or saddle shaped (a few, mostly over the midrib); mostly cross shaped and butterfly shaped.

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

C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles (one large solitary bundle, or one large bundle with two smaller laterals, depending on interpretation); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (but the girders short); nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 1 species (A. burttii).

Distribution, phytogeography, ecology. Tropical East Africa.

Mesophytic; species of open habitats. Savanna, in seasonally wet soils.

References, etc. Morphological/taxonomic: Hubbard 1936b. Leaf anatomical: studied by us.

Illustrations. • A. burttii, abaxial epidermis of leaf blade, microhair: original

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.’.