The grass genera of the world
Tragus: from Dioscorides, perhaps via the Greek tragos (he-goat), because the rigid hairs on the leaves and the bristles on the spikelets reminded the author of a goats beard.
Habit, vegetative morphology. Annual, or perennial; stoloniferous, or decumbent (usually creeping). Culms 5–65 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; slightly cordate, or not cordate, not sagittate; not setaceous (somewhat rigid, the margins pectinate); flat; without abaxial multicellular glands; without cross venation; persistent; rolled in bud. Ligule present; a fringed membrane (very narrow), or a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (with one or more members of the cluster reduced).
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (a spicate raceme of crowded glomerules, the latter very shortly- or rarely long- peduncled, each with 2–5 spikelets); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes very much reduced (to the glomerules); disarticulating; falling entire (the clusters falling whole). Spikelets not secund; sessile to subsessile.
Female-fertile spikelets. Spikelets 2–5 mm long; adaxial; compressed dorsiventrally; falling with the glumes (in the cluster). Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes one per spikelet, or two; very unequal; exceeding the spikelets; (the G2) long relative to the adjacent lemmas (equalling the spikeleta); free; dorsiventral to the rachis; pointed (acute or acuminate); awnless; non-carinate; very dissimilar (the lower tiny, scarious or absent, the upper large, hard, with 5 rows of hooked spines on the back). Lower glume 0 nerved. Upper glume 5–7 nerved; prickly. Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas lanceolate, acute or acuminate; less firm than the glumes (membranous); not becoming indurated; entire; pointed; awnless; hairy (with minute spinous bristles, all over or only centrally); non-carinate; 3 nerved. Palea present; entire (pointed); not indurated (hyaline, glabrous); 2-nerved. Lodicules present; 2; free; fleshy; glabrous; toothed. Stamens 3. Anthers 0.4–0.7 mm long; not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally, or not noticeably compressed. Hilum short. Pericarp fused. Embryo large; not waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.
Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; supine; 6–12 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent; intercostal. Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present, or absent; when present, elongated; clearly two-celled; when present, chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 30 microns long. Microhair total length/width at septum 2.5. Microhair apical cell/total length ratio 0.3. Stomata common; 25–30 microns long. Subsidiaries low dome-shaped, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (rarely), or absent or very rare; silicified, or not silicified. Intercostal silica bodies absent, or imperfectly developed; when present, crescentic. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped (mostly), or crescentic (a few); not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present. Maximum number of extension cells 1. PCR cell chloroplasts with well developed grana; centripetal. Mesophyll with radiate chlorenchyma. Leaf blade nodular in section, or adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Culm anatomy. Culm internode bundles in one or two rings, or in three or more rings.
Cytology. Chromosome base number, x = 10. 2n = 20 and 40. 2 and 4 ploid. Chromosomes small.
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. 7 species; 6 in warm Africa, 1 pantropical. Commonly adventive. Mesophytic to xerophytic; species of open habitats; glycophytic. Often in disturbed ground.
Holarctic, Paleotropical, Neotropical, Cape, and Australian. Boreal, Tethyan, and Madrean. African, Madagascan, and Neocaledonian. Euro-Siberian and Atlantic North American. Macaronesian, Mediterranean, and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, and Namib-Karoo. Caribbean, Central Brazilian, Pampas, and Andean. North and East Australian and Central Australian. European. Southern Atlantic North American. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian and Temperate and South-Eastern Australian.
Rusts and smuts. Rusts Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae Sphacelotheca and Ustilago.
Economic importance. Significant weed species: T. berteronianus, T. racemosus, T. roxburghii.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • General morphology (T. australianus). • General aspect (T. berteronianus). • Close-up of a spikelet cluster (T. australianus). Tragus australianus. Shortly pedunculate glomerule of spikelets, lower glumes spiny. • Abaxial epidermis of leaf blade (T. australianus)
This description is offered for casual browsing only. We strongly advise against extracting comparative information from it. This is much more easily achieved using 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 specified attributes, summaries of attributes within groups of taxa, geographical distribution, classification, and species sampled for anatomy.
Cite this publication as: ‘Watson, L., 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: 18th December 2012. http://delta-intkey.com’.