The grass genera of the world
~ Oropetium (O. aristatum (Stapf) Pilger, = sect. Lepturella)
Habit, vegetative morphology. Dwarf, cushion forming annual; caespitose. Culms 2–9 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes hollow. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; about 2 mm wide (to 4 cm long); usually rolled; exhibiting multicellular glands abaxially (base of macrohairs). The abaxial leaf blade glands on the blade margins. Leaf blades without cross venation; disarticulating from the sheaths, or persistent. Ligule an unfringed membrane (laciniate, with only a few hairs), or a fringed membrane; truncate; about 0.2 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (straight or curved, cylindrical, slender, short). Primary inflorescence branches 1 (i.e., solitary spikes). Rachides hollowed. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes spikes; disarticulating; disarticulating at the joints (into segments each with one spikelet). Articles non-linear; disarticulating transversely; glabrous. Spikelets solitary; not secund; distichous (the ranks opposite); sessile.
Female-fertile spikelets. Spikelets 2.5–3.5 mm long; adaxial; compressed laterally; falling with the glumes (and with the joint); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present (short). Callus short.
Glumes two, or one per spikelet (the G1 reduced or missing, save in the terminal spikelet); very unequal (save in the terminal spikelets, which have equal glumes); exceeding the spikelets; (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; awned (G2 tapered into a long subule); carinate; very dissimilar (G1 a scarious scale or missing, G2 large, covering the floret, awned, rigid). Lower glume 0 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; incised; 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus; non-geniculate; hairless (scabrous); about as long as the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairless; without a germination flap; 3 nerved. Palea present (oblong); relatively long; entire; with apical setae (the keels shortly excurrent); membranous; not indurated; 2-nerved; 2-keeled. Palea keels wingless; glabrous. Lodicules present; 2; free; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2; brown.
Fruit, embryo and seedling. Fruit compressed laterally. Hilum short. Pericarp fused. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. 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. Microhair basal cells 12 microns long. Microhair total length/width at septum 2. Microhair apical cell/total length ratio 0.5. Stomata common. Intercostal short-cells in cork/silica-cell pairs; silicified. Intercostal silica bodies imperfectly developed; tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped; not sharp-pointed (to squarish).
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with the traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles. The lamina margins without fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): cf. Chloridoideae; Cynodonteae; cf. Tripogoninae. 1 species (L. aristata).
Distribution, phytogeography, ecology. West tropical Africa.
Mesophytic to xerophytic; species of open habitats; glycophytic.
References, etc. Leaf anatomical: Metcalfe 1960; Van den Borre 1994; studied by us - L. aristata Stapf.
Illustrations. • L. aristata: Jacques-Félix, 1962
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’.