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From the Greek treis (three) and pogon (beard), referring to hairs at the base of the three lemma nerves.
Type species: T. bromoides Roem. & Schult.
Including Archangelina Kuntze, Kralikia Coss. & Dur., Kralikiella Batt. & Trab., Plagiolytrum Nees
Excluding Oropetium
Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 4–65 cm high; herbaceous; where recorded, unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades linear (often filiform); narrow; setaceous, or not setaceous; not needle-like; without abaxial multicellular glands; without cross venation; persistent. Ligule an unfringed membrane to a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (slender). Rachides hollowed. Spikelets all partially embedded in the rachis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; alternately distichous; sessile; not imbricate.
Female-fertile spikelets. Spikelets 3–25 mm long; adaxial; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous); the rachilla extension with incomplete florets. Hairy callus present (minute). Callus short.
Glumes two; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas to long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; glabrous; awnless; carinate; very dissimilar, or similar (membranous, narrow, the G1 often asymmetric). Lower glume 1 nerved. Upper glume 1 nerved, or 3 nerved, or 5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (or rarely, the L1 also neuter). The distal incomplete florets merely underdeveloped.
Female-fertile florets 3–20. Lemmas not becoming indurated (scarious with hyaline margins); 2 lobed, or 4 lobed; not deeply cleft (the teeth small); mucronate, or awned (usually awned or mucronate from a median sinus or behind the apex, the lobes sometimes awned or mucronate). Awns when present, 1, or 3, or 5; median, or median and lateral (via mucronate to awned lobes); the median similar in form to the laterals (when laterals present); from a sinus, or apical; non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; glabrous; carinate; 1–3 nerved. Palea present; entire (truncate), or apically notched; awnless, without apical setae; not indurated (hyaline); 1-nerved, or 2-nerved; 2-keeled. Palea keels usually winged (below). Lodicules present; 2; free; fleshy; glabrous. Stamens 2, or 3. Anthers 0.8–1.3 mm long; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (0.8–2.2 mm long); not noticeably compressed (terete), or trigonous. Hilum short. Pericarp fused. Embryo large, or small (1/3 the length of the fruit or somewhat less). Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
First seedling leaf with a well-developed lamina.
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; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 16.5–21 microns long. Microhair basal cells 2.4–3.6 microns long. Microhairs 9–12 microns wide at the septum. Microhair total length/width at septum 1.6–2. Microhair apical cells 10.5–12(–13.5) microns long. Microhair apical cell/total length ratio 0.58–0.67. Stomata common; 18–21 microns long. Subsidiaries dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; in cork/silica-cell pairs; silicified. Intercostal silica bodies imperfectly developed. 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 and tall-and-narrow (or rectangular); 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 absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade ‘nodular’ in section, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only. Bulliforms associated with colourless mesophyll cells to form deeply-penetrating fans (these sometimes linking with traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Phytochemistry. Leaves without flavonoid sulphates (1 species).
Cytology. Chromosome base number, x = 10. 2n = 20. Chromosomes ‘small’.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Tripogoninae. About 30 species.
Distribution, phytogeography, ecology. Tropical Africa, Asia, Australia.
Helophytic to xerophytic; species of open habitats; glycophytic.
Rusts and smuts. Rusts — Puccinia.
References, etc. Morphological/taxonomic: Phillips and Launert 1971. Leaf anatomical: Metcalfe 1960; studied by us - T. loliiformis (Muell.) Hubbard.
Illustrations. • Tripogon spicatus: Nicora & Rúgolo de Agrasar (1987). • General aspect, inflorescence, spikelet (Tripogon loliiformis). • General aspect (Tripogon minimus): Gibbs Russell et al., 1990. • Tripogon loliiformis, 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: 25th January 2024. delta-intkey.com’.
