The grass genera of the world
Habit, vegetative morphology. Robust perennial; rhizomatous and caespitose. The flowering culms leafy. Culms 100–350 cm high; herbaceous; unbranched above. Pluricaespitose. Plants unarmed. Leaves not basally aggregated. Leaf blades linear; broad; 10–30 mm wide (and to 1.2 m long); flat; not pseudopetiolate; without cross venation. Ligule an unfringed membrane; not truncate (ovate-lanceolate); 15–80 mm long.
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 males below the females on the same panicle branches). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence paniculate (large, to 100 cm or more long); open; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-sterile spikelets. Male spikelets sometimes larger, with 7-nerved lemma, 2-nerved palea and 6 free, non-penicillate stamens. The male spikelets without glumes; 1 floreted. Male florets 6 staminate. The staminal filaments free.
Female-fertile spikelets. Spikelets unconventional (through lacking glumes); 6–8 mm long; subcylindrical, or elliptic, or lanceolate, or ovate; compressed laterally to not noticeably compressed; disarticulating from the pedicels. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes absent. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas lanceolate, tapered into the awn; entire; pointed; awned. Awns 1; median; apical; non-geniculate; hairless; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas 5–7 nerved. Palea present; relatively long; entire (narrow, pointed); several nerved (3); one-keeled. Stamens 0. Ovary apically glabrous. Styles fused (into one long style). Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; medium sized (6–7 mm long); not noticeably compressed (cylindrical). Hilum long-linear. Endosperm hard; without lipid.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata (in places), or not over-arching the stomata (elsewhere); several per cell (most cells in Z. bonariense with a median row of thick walled, circular or bifurcated papillae, and often with a single very large papilla in addition; long-cells in Z. miliacea with 2 or 3 irregular rows of small, thick walled, circular papillae, which tend to associate with those of the interstomatals to encircle the stomata). Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals more regularly rectangular); of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (the sinuosity coarse to fairly fine). Microhairs present; elongated; ostensibly one-celled; of peculiar form - small to medium sized, thin walled, pyriform with pointed tips, and bent over. Stomata common; 24–27 microns long (Z. miliacea), or 36–39 microns long (Z. bonariensis). Subsidiaries non-papillate; dome-shaped and triangular (mostly low domes, in Z. bonariensis). Guard-cells overlapped by the interstomatals (slightly). Intercostal short-cells common; in cork/silica-cell pairs; silicified, or not silicified. Intercostal silica bodies oryzoid-type, or vertically elongated-nodular (in Z. miliacea, ill-defined in Z. bonariensis). Costal zones with short-cells. Costal short-cells conspicuously in long rows (Z. miliacea), or predominantly paired (Z. bonariensis). Costal silica bodies oryzoid; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+ (the mestome sheath heavily lignified, often double). Mesophyll without adaxial palisade; without arm cells (seemingly, in the poor material seen), or without arm cells (?); with fusoids. The fusoids external to the PBS. Leaf blade with distinct, prominent adaxial ribs to nodular in section. Midrib conspicuous; having complex vascularization; with colourless mesophyll adaxially (and with large areas of stellate aerenchyma). The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans (the fans large). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (every bundle with an I or an anchor). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid. Nucleoli persistent.
Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Oryzeae. Soreng et al. (2015): Oryzoideae; Oryzeae; Zizaniinae. 5 species.
Distribution, phytogeography, ecology. Southern U.S.A., South America.
References, etc. Leaf anatomical: this project.
Illustrations. • Z. bonariensis: Nicora & Rúgolo de Agrasar (1987)
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: 13th November 2017. delta-intkey.com/grass’.