Tripogon Roem. & Schult.
From the Greek treis (three) and pogon (beard), referring to hairs at the base of the three lemma nerves.
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; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades linear (often filiform); narrow; setaceous, or not setaceous; without abaxial multicellular glands; without cross venation; persistent; an unfringed membrane to a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (slender). Rachides hollowed. 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. Spikelets without proximal incomplete florets.
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 glabrous; without a conspicuous apical appendage. 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’.
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. About 30 species; tropical Africa, Asia, Australia. Helophytic to xerophytic; species of open habitats; glycophytic.
Holarctic, Paleotropical, Neotropical, and Australian. Boreal and Tethyan. African and Indomalesian. Euro-Siberian, Eastern Asian, and Atlantic North American. Macaronesian and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, and Papuan. Central Brazilian, Pampas, and Andean. North and East Australian and Central Australian. Siberian. Southern Atlantic North American and Central Grasslands. 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.
References, etc. Morphological/taxonomic: Phillips and Launert 1971. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • General aspect, inflorescence, spikelet. • General aspect
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
