The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. The flowering culms leafy. Culms 7–19 cm high; herbaceous; branched above. Culm nodes glabrous. Young shoots intravaginal. Leaves not basally aggregated; auriculate (the sheath being extended upwards into a single, median, prominent auricle, with which the ligule is marginally adnate); without auricular setae (the auricle glabrous or sparsely hairy). Leaf blades ovate to elliptic; broad; 8–16 mm wide; flat; conspicuously pseudopetiolate; cross veined; persistent (seemingly); rolled in bud. Ligule present to absent.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (male and female); female-only and male-only (the males fewer, peripheral in the inflorescence). The male and female-fertile spikelets on different branches of the same inflorescence to segregated, in different parts of the same inflorescence branch (the males terminating the main axis and the major branches, or the lower branches sometimes exclusively female). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence paniculate; open; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate (the pedicels 3–14 mm long).
Female-sterile spikelets. Male spikelets 3–6.4 mm long, sometimes with a linear upper glume, 1–4 flowered, lemmas glabrous, stamens 2 or 3, or 2 plus a staminode, anthers 1.5–2 mm long, not penicillate, unappendaged; lodicules 2, fleshy, inconspicuously vascularised. The male spikelets with glumes (one), or without glumes; 1–4 floreted. Male florets 2 staminate, or 3 staminate (or two plus a staminode).
Female-fertile spikelets. Spikelets unconventional (being without glumes); 2.3–3 mm long; falling entire. Rachilla terminated by a female-fertile floret (?). Hairy callus absent. Callus absent.
Glumes absent. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas herbaceous; not becoming indurated; entire, or incised; when incised, minutely 3 lobed; not deeply cleft; awnless; hairy (between the nerves); non-carinate (seemingly- slightly sulcate between the nerves); without a germination flap; 5 nerved, or 7 nerved; with the nerves non-confluent. Palea present; relatively long (slightly shorter than the lemma); apically notched; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled (hairy between the keels). Lodicules present; 2; joined to free; fleshy; glabrous; not or scarcely vascularized (obscurely vascularised). Stamens 0 (sometimes with two minute staminodes). Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small (about 1.8 mm long); compressed laterally. Hilum short (apparently). Embryo large (about 1/3 of the caryopsis length).
Abaxial leaf blade epidermis. Papillae present. Intercostal papillae over-arching the stomata; several per cell (2 to 3 per intercostal long-cell, sometimes branched, large, covering over much of the epidermis). Intercostal zones without typical long-cells (these being generally only slightly longer than wide). Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries dome-shaped and triangular. Costal silica bodies panicoid-type, or oryzoid and panicoid-type (?); cross shaped and dumb-bell shaped (? -described as irregular dumb-bells with somewhat angular and indented ends, and very small, narrow crosses); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; with adaxial palisade; without arm cells; without fusoids. Leaf blade adaxially flat (apart from a conspicuous adaxial mid rib). Midrib conspicuous; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (the entire epidermis being bulliform). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (in all the primary bundles save the midrib, which has an adaxial strand). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid.
Classification. Watson & Dallwitz (1994): Centothecoideae; Centotheceae. Soreng et al. (2015): Panicoideae; Zeugiteae. 1 species (P. petiolatum).
Distribution, phytogeography, ecology. Panama.
Helophytic; shade species.
References, etc. Morphological/taxonomic: Davidse, Soderstrom and Ellis 1986.
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’.