The grass genera of the world
Habit, vegetative morphology. Annual, or perennial (usually delicate, often with coloured leaves, culms and spathes); caespitose. Culms sparsely to amply branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes hollow. The shoots aromatic (from conspicuous glands on the leaves and spathes), or not aromatic (rarely). Leaves not basally aggregated; non-auriculate. Leaf blades narrow; flat, or folded; without cross venation; persistent. Ligule a fringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets (usually), or without hermaphrodite florets (rarely). The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile, or female-only and male-only, or female-only and sterile; overtly heteromorphic; in both homogamous and heterogamous combinations (with two basal pairs of homogamous, male or sterile spikelets, connate to form a false tetramerous whorl beneath the single heterogamous triplet).
Inflorescence. Inflorescence falsely paniculate (the single racemes or tight clusters gathered with their spatheoles into a narrow false panicle); open; spatheate; a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes very much reduced (with small, short spike-like racemes, similar to Themeda but disarticulating below the involucral spikelets); disarticulating; falling entire (complete with the involucral spikelets, and sometimes with the investing spatheole, which may then be indurated). Spikelets associated with bractiform involucres (comprising the involucral spikelets). The involucres (i.e. the involucral spikelets) shed with the fertile spikelets. Spikelets distal to the involucral whorl in triplets; not secund; sessile and pedicellate (two pedicellate members per heterogamous triplet, the pedicels filiform); consistently in long-and-short combinations; in pedicellate/sessile combinations. The shorter spikelets hermaphrodite, or female-only. The longer spikelets male-only, or sterile.
Female-sterile spikelets. The two basal pairs of spikelets homogamous, male or sterile, all more or less pedicelled, connate into a tetramerous false whorl beneath the single heterogamous triplet, often indurated.
Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes (and with the whole racemelet. the upper pedicellate pair usually smaller than the sessile,sometimes much reduced, deciduous or not). Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.
Glumes two; more or less equal; long relative to the adjacent lemmas; awnless. Lower glume not two-keeled; flattened on the back; not pitted; relatively smooth; 8–10 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved, or 3 nerved; exceeded by the female-fertile lemmas; not becoming indurated (hyaline).
Female-fertile florets 1. Lemmas stipitate beneath the awn; less firm than the glumes; not becoming indurated; entire, or incised; when incised, 2 lobed; awned. Awns 1; median; from a sinus, or apical; geniculate. Lemmas hairless; non-carinate; without a germination flap; 1 nerved. Palea absent. Lodicules present; 2; fleshy. Stamens 1–3. Anthers not penicillate. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell (not all the cells being papillate). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 57–63 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 10.5–11.1. Microhair apical cells 31.5–37.5 microns long. Microhair apical cell/total length ratio 0.51–0.63. Stomata common; 24–25.5 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; in cork/silica-cell pairs, or not paired (solitary); silicified (when paired), or not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped and dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 4, or 5 (?). 2n = 6, 8, 18, 28, and 36. 2, 7, and 9 ploid (?).
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 20 species.
Distribution, phytogeography, ecology. Indomalayan region, Australia.
Species of open habitats. Grassland.
Economic aspects. Important native pasture species: I. vaginiflorum.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae Sorosporium, Sphacelotheca, and Ustilago.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • I. vaginiflorum: Gardner, 1952. • Inflorescence and spikelet details (6 Australian species): Gardner, 1952. • I. vaginiflorum, abaxial epidermis of leaf blade: 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: 13th November 2017. delta-intkey.com/grass’.