The grass genera of the world
Habit, vegetative morphology. Perennial; densely caespitose. Culms 50–80 cm high; herbaceous (erect, stiff); unbranched above; 6–10 noded. Culm nodes exposed; glabrous (dark). Culm internodes hollow (glabrous, stramineous). Young shoots intravaginal. Leaves not basally aggregated (basal and cauline); non-auriculate. Sheaths dorsally rounded, glabrous. Leaf blades linear; narrow; 0.5–1 mm wide (10–20 cm long); setaceous; rolled to acicular (U-shaped in section below, nearly cylindrical distally, the apex subpungent); without cross venation; disarticulating from the sheaths to persistent. Ligule a fringe of hairs (minute); 0.5 mm long (with hairs to 6.5 mm long behind).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets hermaphrodite.
Inflorescence. Inflorescence of spicate main branches, or a false spike, with spikelets on contracted axes, or a single raceme (the 6–10 cm long, delicate, erect or drooping, spikelike racemes one terminal and usually one axillary at the tops of the culms, well exserted on 6–22 cm long peduncles); contracted; spicate; digitate, or non-digitate. Primary inflorescence branches 1, or 2. Inflorescence axes not ending in spikelets (the rachis apex extending beyond the spikelets as a sterile projection to 5 mm long). Rachides flattened and winged (the membranous wings 0.-1.1 mm wide). Inflorescence spatheate (the axillary raceme prophyllate), or espatheate; a complex of partial inflorescences and intervening foliar organs, or not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund (the rachides unilateral); biseriate (borne alternately on each side of the midrib); subsessile (the pedicels adnate to the rachis midrib for most of their length); imbricate.
Female-fertile spikelets. Spikelets somewhat unconventional (owing to the lack of a lower glume, combined with the peculiar structure of the lemma of the lower floret); 2.3–3.1 mm long (and 0.4–0.5 mm wide); narrowly elliptic to lanceolate; adaxial (i.e. the only, upper glume being abaxial); compressed dorsiventrally; falling with the glumes; not disarticulating between the florets; with conventional internode spacings. The upper floret not stipitate. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus blunt.
Glumes one per spikelet; relatively large; about equalling the spikelets; long relative to the adjacent lemmas (the colourless glume embracing the upper floret, but leaving the lower lemma free); dorsiventral to the rachis; hairless; scabrous (with conspicuous prickle hairs); pointed (acute); awnless; non-carinate. Upper glume i.e. the single glume, indistinctly 2 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate (this seeming the best interpretation, despite resulting in a binerved lemma); sterile. The proximal lemmas of peculiar, narrow form, having a central hyaline portion bordered by well developed, conspicously ciliate and terminally setose nerves, the whole being reminiscent of a Bothriochloa pedicel; awnless (but with a striking pair of terminal, cushion-based, 5–7 mm long setae, which are hygroscopically active and awnlike); 2 nerved; somewhat exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas to decidedly firmer than the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas similar in texture to the glumes; not becoming indurated (membranous save for the hyaline apex, by contrast with the heavy margins of the lower lemma); copper-coloured; entire; pointed (acute); awnless; hairless (with a few prickle hairs and microhairs only); non-carinate; having the margins inrolled against the palea (below, but flat and free from the palea at the tip); without a germination flap; indistinctly nerved. Palea present; relatively long (about equalling the lemma); gaping (at the tip); apically notched; awnless, without apical setae; thinner than the lemma (hyaline); not indurated; 2-nerved. Lodicules present; 2; free; fleshy; glabrous (?). Stamens 2 (usually), or 3 (rarely). Anthers 1.3–1.7 mm long (purple); not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white (or rather, yellow), or red pigmented (varying in the same inflorescence).
Fruit, embryo and seedling. Fruit small (1–1.2 mm long); wine-red; narrowly obovate to clavate; not grooved. Hilum short. Embryo large (about half the caryopsis length); not waisted.
Transverse section of leaf blade, physiology. Leaf blades seemingly consisting of midrib.
C4; XyMS. PCR sheath outlines even. PCR sheath extensions absent. Mesophyll without adaxial palisade. Midrib conspicuous, in that the blade appears largely reduced to midrib, with a single group of large bulliforms occupying the shallow adaxial groove; having a conventional arc of bundles; with colourless mesophyll adaxially. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent (the sclerenchyma seemingly limited to abaxial girders with the larger byndles). Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. The lower lemma narrow, of peculiar form, having a central hyaline portion bordered by well developed, conspicously ciliate and terminally setose nerves (the whole being reminiscent of a Bothriochloa pedicel), and exhibiting apically a pair of cushion-based, 57 mm long, hygroscopically active and awnlike setae.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Paspalinae. 1 species (O. hydrolithica).
Distribution, phytogeography, ecology. Brazil.
Glycophytic. On serpentine (ophiolite) rocks, in seasonally running water.
References, etc. Morphological/taxonomic: Filgueiras, Davidse and Zuloaga 1993. Leaf anatomical: Filgueiras, Davidse and Zuloaga 1993.
Special comments. Probably another odd Digitaria relative, as assigned by Filgueiras et al., although a preliminary INTKEY exploration based on this description suggests there is as much in common with Paspalum and even with some Andropogoneae (Rottboelliinae, e.g. Phacelurus). Anatomical data for ts only.
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’.