The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose, or decumbent (or vine-like, or clambering). The flowering culms leafy. Culms 30–160 cm high (or trailing and climbing and up to 10 m long); woody and persistent to herbaceous; scandent, or not scandent; decumbent, scrambling, and scandent; sparsely branched above. The branching simple. Culm nodes hairy (pilose, with retrorse hairs). Culm internodes hollow. Leaves not basally aggregated; non-auriculate; without auricular setae. Sheaths glabrous to pilose. Leaf blades lanceolate to ovate; broad; 25–130 mm wide; slightly cordate, or not cordate, not sagittate; flat; pseudopetiolate; cross veined, or without cross venation (?); disarticulating from the sheaths; rolled in bud. Ligule an unfringed membrane to a fringed membrane; truncate.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets on different branches of the same inflorescence, or segregated, in different parts of the same inflorescence branch (the lower branches with male spikelets only, the upper branches male basally and female terminally or female-only: cf. Olyra). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence determinate, or indeterminate; paniculate; open (lax and diffuse); probably spatheate (cf. Olyra). Spikelets solitary; not secund; pedicellate (the pedicels filiform, by contrast with Olyra).
Female-sterile spikelets. The male spikelets without glumes, stamens 3. Rachilla of male spikelets terminated by a male floret. The male spikelets without glumes; without proximal incomplete florets; 1 floreted. Male florets 1; 3 staminate.
Female-fertile spikelets. Spikelets 2–5.8 mm long; compressed dorsiventrally; falling with the glumes; with a distinctly elongated rachilla internode between the glumes (this prominent and thickened). Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.
Glumes present; two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; conspicuously ventricose (inflated to indurate at maturity); hairy (shortly pilose); awnless; non-carinate; similar (membranous, inflated). Lower glume 5–9 nerved. Upper glume 3–6 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1 (the anthecium resembling that typical of Paniceae). Lemmas decidedly firmer than the glumes; smooth (shining); becoming indurated; entire; pointed, or blunt; awnless; hairy, or hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; indurated; 2-nerved; keel-less. Lodicules present; 3; free; glabrous; heavily vascularized. Stamens 0. Ovary apically glabrous. Styles fused (into one). Stigmas 2.
Fruit, embryo and seedling. Disseminule a caryopsis enclosed in but free of the lemma and palea. Fruit free from both lemma and palea; small (1–2.5 mm long); brownish; ellipsoid; compressed dorsiventrally. Hilum long-linear (but markedly shorter than the caryopsis, by contrast with Olyra). Pericarp fused. Embryo small. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; costal and intercostal. Intercostal papillae not over-arching the stomata; several per cell (small, circular, with one or two irregular rows per long-cell in P. ramosissima, larger in P. lateralis, very variable in size and number and some very large and branched in P. leutzelburgii). Mid-intercostal long-cells rectangular; having markedly sinuous walls (with coarse sinuosity). Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries papillate; high dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitary in P. leutzelburgii); silicified. Intercostal silica bodies vertically elongated-nodular. Bulbous-based prickles common. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; consistently angular cross shaped.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; with arm cells; with fusoids, or without fusoids (none seen in P. lateralis). The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous to not readily distinguishable (sometimes with a somewhat raised, rounded adaxial rib); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (the groups large, in each mid-intercostal region); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (all the bundles with anchors). Sclerenchyma all associated with vascular bundles.
Cytology. 2n = 36.
Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 3 species.
Distribution, phytogeography, ecology. From Costa Rica south to Bolivia and Bahia, Brazil.
Mesophytic; shade species and species of open habitats; glycophytic. In low and mid-elevation forests and savannas.
References, etc. Morphological/taxonomic: Soderstrom and Zuloaga 1989. Leaf anatomical: studied by us - P. lateralis (Presl) Soderstrom & Zuloaga, P. luetzelburgii (Pilger) Soderstrom & Zuloaga, P. ramosissima (Trin.) Soderstrom & Zuloaga.
Illustrations. • P. micrantha, as Olyra: Kunth (1835). • P. micrantha, as Olyra: Lamson-Scribner (1890). • P. ramosissima, abaxial epidermis of leaf blade: this project. • P. ramosissima, abaxial epidermis of leaf blade: this project. • Abaxial epidermis of leaf blade of P. luetzelburgii: 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. delta-intkey.com/grass’.