The grass genera of the world
Habit, vegetative morphology. Annual. Culms 5–60 cm high; herbaceous. Culm internodes hollow. Leaves not basally aggregated; auriculate (the auricles small). Leaf blades linear; narrow; 0.3–4 mm wide; flat, or rolled (convolute); without cross venation. Ligule present (short); an unfringed membrane; truncate; 0.2–0.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile (sterile at the tip of the rachis). Viviparous (sometimes), or not viviparous.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the clusters reduced to spikelet pairs); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; not secund; distichous; sessile.
Female-fertile spikelets. Spikelets 8–15 mm long; compressed dorsiventrally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (slightly scabrid, flattened between the florets); the rachilla extension with incomplete florets. Hairy callus absent. Callus long; pointed (with only a few marginal spicules).
Glumes two; very unequal to more or less equal; joined; hairless; scabrous; subulate; awned (awn-like); similar (indurated at the base). Lower glume 1 nerved, or 3 nerved. Upper glume 1 nerved, or 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets usually 1; merely underdeveloped.
Female-fertile florets 1. Lemmas attenuate to the awn; less firm than the glumes to similar in texture to the glumes; entire; pointed; awned. Awns 1; median; apical; non-geniculate; recurving; hairless (scabrid); much longer than the body of the lemma (4–12 cm long); entered by several veins. Lemmas hairless; scabrous; non-carinate; without a germination flap; 5 nerved. Palea present; relatively long (about equalling the lemma); entire (obtuse), or apically notched (slightly); 2-nerved; 2-keeled (scabrid on the keels). Lodicules present; 2; free; membranous; ciliate; toothed; not or scarcely vascularized. Stamens 3. Anthers 0.6–1.4 mm long (relatively short). Ovary apically hairy; with a conspicuous apical appendage (fleshy below the styles). Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit somewhat adhering to lemma and/or palea; medium sized (6–9 mm long); longitudinally grooved; compressed dorsiventrally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo small. Endosperm hard; without lipid; containing only simple starch grains. Embryo with an epiblast, or without an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally (quite thick walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs absent. Stomata common; 28–33 microns long. Subsidiaries dome-shaped (mostly, low), or parallel-sided. Guard-cells overlapped by the interstomatals (but at the most very slightly), or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (mostly); silicified. Intercostal silica bodies rounded to crescentic. Crown cells present. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded, or crescentic; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (wide, rounded). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (in T. caput-medusae). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Haplomic genome content T. Chromosomes large. Haploid nuclear DNA content 4.4 pg (1 species). Mean diploid 2c DNA value 8.8 pg.
Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 1 species (T. caput-medusae, with synonyms crinitum and asperum).
Distribution, phytogeography, ecology. Mediterranean to northwest India.
Commonly adventive. Xerophytic.
Economic aspects. Important native pasture species: T. asperum, T. crinitum.
Hybrids. Intergeneric hybrid with Triticum aestivum. Sterile hybrids made with Hordeum and Aegilops.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia striiformis and Puccinia hordei. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae Tilletia. Ustilaginaceae Ustilago.
References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • T. caput-medusae, as Elymus: Hitchcock & Chase (1959). • T. caput-medusae, 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’.