| | The grass genera of the world |
From the Greek treis (three) and raphis (a needle), referring to the three-awned lemmas.
Type species: Type: T. mollis R.Br.
Habit, vegetative morphology. Annual, or perennial; caespitose (mostly small xeromorphs). Culms (1–)4–140 cm high; herbaceous; branched above (amply, in T. ramosissima), or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes solid. Leaves mostly basal; non-auriculate. Leaf blades narrow; setaceous, or not setaceous; flat, or rolled (or junciform); without abaxial multicellular glands; not pseudopetiolate; without cross venation; persistent. Ligule a fringed membrane, or a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open, or contracted (rarely spiciform); when contracted, spicate to more or less irregular; with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present.
Glumes two; relatively large; very unequal (rarely), or more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; pointed, or not pointed (often bidentate); awned (or mucronate, from the sinus), or awnless; carinate; similar (narrow, persistent). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 3–10. Lemmas not becoming indurated (membranous); incised; 3 lobed, or 4 lobed (when the central lobe is bidentate); deeply cleft (on either side of the central lobe); awned. Awns 3; median and lateral (the lateral lobes setiform-awned or mucronate); the median similar in form to the laterals; from a sinus (of the central lobe); non-geniculate (setiform). The lateral awns shorter than the median. Lemmas hairy (villous on the lateral nerves); non-carinate (3-keeled), or carinate (when the lateral keels are near the margins); 3 nerved. Palea present; shorter than the lemma; apically notched, or deeply bifid; not indurated (hyaline); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy, or membranous; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; linear; trigonous. Hilum short. Pericarp fused. Embryo large; waisted. Endosperm 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.
First seedling leaf with a well-developed lamina. The lamina broad (fairly); curved.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. 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; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs without ‘partitioning membranes’ (in T. mollis); (40–)50–72(–75) microns long; (6–)6.6–7.5(–8.4) microns wide at the septum. Microhair total length/width at septum 6.8–11. Microhair apical cells (27–)30–42(–46) microns long. Microhair apical cell/total length ratio 0.44–0.63. Stomata common; (24–)25–31.5(–36) microns long. Subsidiaries parallel-sided and dome-shaped, or dome-shaped and triangular, or parallel-sided, dome-shaped, and triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal zones with short-cells. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped to butterfly shaped, or dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; biochemical type NAD–ME (T. mollis, although exhibiting ‘PCK-like’ leaf blade anatomy); XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions present. Maximum number of extension cells 3. PCR cells with a suberised lamella. PCR cell chloroplasts ovoid; with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size, or with the ribs very irregular in sizes. Midrib conspicuous, or not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (in T. pumilio, according to Metcalfe 1960). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Leaf blade chlorophyll a:b ratio 4–4.01.
Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Triraphideae. 7 species.
Distribution, phytogeography, ecology. Tropical and southern Africa, Australia.
Mesophytic to xerophytic; species of open habitats; glycophytic. Savanna, in sandy or rocky soil.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - T. mollis R. Br.
Illustrations. • General aspect (T. andropogonoides): Gibbs Russell et al., 1990. • Triraphis mollis: Gardner, 1952. • Inflorescence of Triraphis mollis. • Spikelet of T. mollis. • T. mollis spikelet with glumes removed. • Detail of lemma tip of T. mollis. • Triraphis mollis, abaxial epidermis of leaf blade: this project. • Triraphis mollis, T.S. of leaf blade midrib region: 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: 25th January 2024. delta-intkey.com’.
