| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Trachypogon Nees

From the Greek trachus (rough) and pogon (beard), referring to awns of female-fertile spikelets.

Including Homopogon Stapf

Habit, vegetative morphology. Slender perennial (very rarely annual); caespitose. Culms 30–200 cm high; herbaceous; unbranched above. Culm nodes hairy (with white hairs). Leaves non-auriculate. Leaf blades linear; narrow; not setaceous; rolled (usually, convolute), or flat (sometimes). Ligule an unfringed membrane; not truncate.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; more or less overtly heteromorphic (the male or neuter spikelets without a callus, often awnless); all in heterogamous combinations.

Inflorescence. Inflorescence of spicate main branches, or a single raceme; digitate, or non-digitate (when unbranched); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (long, terminating the culms); solitary, or paired, or clustered (up to 5 ‘racemes’); persistent (but the joints articulated and usually shortly bearded). ‘Articles’ not appendaged; oblique. Spikelets paired; pedicellate; consistently in ‘long-and-short’ combinations (in which the usual pattern of sexuality is inverted); unequally pedicellate in each combination. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets male-only, or sterile. The ‘longer’ spikelets hermaphrodite.

Female-sterile spikelets. The short-pedicelled male or neuter spikelets persistent, sometimes dorsally flattened. Without a callus, often awnless. L1 sterile. Rachilla of male spikelets terminated by a male floret. The male spikelets with proximal incomplete florets. The lemmas awnless. Male florets 1.

Female-fertile spikelets. Spikelets not noticeably compressed (cylindrical); falling with the glumes (falling from the pedicels). Rachilla terminated by a female-fertile floret. Hairy callus present (in the pedicelled members). Callus of the pedicelled members pointed (attached obliquely to the pedicel).

Glumes two; relatively large; more or less equal; long relative to the adjacent lemmas; hairy; without conspicuous tufts or rows of hairs; awnless; carinate (G2), or non-carinate (G1); very dissimilar (the G1 firmer, convolute and 2-keeled, the G2 thinner, channelled on each side of the rounded keel). Lower glume two-keeled; not pitted; relatively smooth; 7–11 nerved (the nerves inconspicuous between the keels, anastomosing above). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 nerved; more or less equalling the female-fertile lemmas; hyaline; not becoming indurated (ciliate above).

Female-fertile florets 1. Lemmas hyaline basally, but becoming stipitate-cartilaginous above; less firm than the glumes; not becoming indurated; entire; not deeply cleft; awned. Awns 1; median; apical; geniculate; hairy to long-plumose; much longer than the body of the lemma. Lemmas hairy; non-carinate; without a germination flap; 3 nerved. Palea present, or absent; when present, very reduced; not indurated (hyaline). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (39–)42–45(–48) microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 7–8.9. Microhair apical cells (18–)24–26(–27) microns long. Microhair apical cell/total length ratio 0.46–0.57. Stomata common; 22.5–27 microns long. Subsidiaries mostly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Bulbous-based costal prickles abundant. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped (some), or dumb-bell shaped (mostly); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS– (but many individual bundles have intervening mestome on one side, or are approaching the XyMS+ condition, and the main midrib bundle is XyMS+). PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (these being the ‘arms’ of bulliform-plus-colourless cell arches). Leaf blade with distinct, prominent adaxial ribs (low, round-topped, over primary bundles). Midrib conspicuous; having a conventional arc of bundles (a large median, and three small laterals on either side); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (linking via colourless cells with the abaxial epidermis); associating with colourless mesophyll cells to form arches over small vascular bundles. All the vascular bundles accompanied by sclerenchyma (even the smallest having minute abaxial strands). Combined sclerenchyma girders present (with the primary laterals); forming ‘figures’ (the primary laterals). Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves containing flavonoid sulphates (1 species, doubtfully), or without flavonoid sulphates (3 species).

Cytology. Chromosome base number, x = 5, or 10. 2n = 20 and 40.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Germainiinae. About 13 species.

Distribution, phytogeography, ecology. Tropical America and Africa, Madagascar.

Mesophytic; species of open habitats; glycophytic. Savanna.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia eritraeensis and Puccinia versicolor. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Ustilago.

References, etc. Leaf anatomical: studied by us - T. plumosus Nees.

Illustrations. • Trachypogon spicatus, as Andropogon mollis: Kunth (1835). • T. spicatus (as T. thollonii): Jacques-Félix, 1962. • General aspect (T. spicatus): Gibbs Russell et al., 1990. • Trachypogon plumosus, abaxial epidermis of leaf blade: this project. • Trachypogon plumosus, 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: 15th June 2025. delta-intkey.com’.

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