| # The grass genera of the world |

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

### Gymnopogon P. Beauv.

From the Greek gumnos (naked) and pogon (beard), alluding to a naked rachilla extension.

Including Anthopogon Nutt., Alloiantheros Elliott ex Raf., Biatherium Desv., Sciadonardus Steud., Monochaete Doell., Doellochloa Kuntze

Habit, vegetative morphology. Annual (rarely), or perennial; caespitose (with short, scaly rhizomes). Culms 20–60 cm high; herbaceous; unbranched above. Leaves not basally aggregated; conspicuously distichous; non-auriculate. Sheaths keel-less. Leaf blades linear to ovate-lanceolate; broad, or narrow; cordate, or not cordate, not sagittate; not setaceous (short, stiff, often folded when dry); without abaxial multicellular glands; pseudopetiolate, or not pseudopetiolate. Ligule a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (except that the lowermost spikelets of the branches may be sterile). Plants exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence of spicate main branches; open; subdigitate to non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base, or without spikelets towards the base. Spikelet-bearing axes persistent. Spikelets solitary (appressed); secund (in two rows along one side of rachis); biseriate; not imbricate.

Female-fertile spikelets. Spikelets 3–6 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus present (short or linear), or absent (?).

Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; free; dorsiventral to the rachis; pointed; awned, or awnless; similar (narrow, acuminate). 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 1, or 2; awned (the terminal rudiment sometimes 2–3 awned). Spikelets without proximal incomplete florets.

Female-fertile florets 1(–3). Lemmas not becoming indurated (membranous); incised; 2 lobed; not deeply cleft (minutely notched); mucronate (rarely), or awned (usually). Awns when present, 1; from a sinus; non-geniculate (?); much shorter than the body of the lemma to about as long as the body of the lemma. Lemmas hairy, or hairless; 3 nerved. Palea present; relatively long; 2-nerved. Ovary apically glabrous. Stigmas probably 2.

Fruit, embryo and seedling. Fruit ellipsoid; compressed dorsiventrally to not noticeably compressed. Hilum short. Endosperm hard; without lipid; containing only simple starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (the intercostal zones very narrow). Papillae present; costal and intercostal. Intercostal papillae not over-arching the stomata; several per cell (on some costal and intercostal long-cells and some interstomatals, small, sometimes obscure). Long-cells of similar wall thickness costally and intercostally (thick walled). Mid-intercostal long-cells rectangular; having straight or only gently undulating walls (distant sinuations). Microhairs present; more or less spherical, or elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs about 19 microns long. Microhair basal cells 6–9 microns long. Microhairs about 7.5 microns wide at the septum. Microhair total length/width at septum 0.25. Microhair apical cells about 12.3 microns long. Microhair apical cell/total length ratio 0.66. Stomata common; 18–21 microns long. Subsidiaries predominantly triangular, or dome-shaped and triangular, or parallel-sided (in G. ambiguus, according to Metcalfe). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (rare, solitary or paired). Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; dumb-bell shaped.

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, or absent. Maximum number of extension cells 1, or 2. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (G. ambiguus), or not traversed by colourless columns (in G. foliosus, none of the columns seems to fully traverse). Leaf blade with distinct, prominent adaxial ribs (the ribs low, round topped); with the ribs more or less constant in size (slight ribs only). 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 (sometimes linked with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (all the bundles with conspicuous anchors). Sclerenchyma all associated with vascular bundles (but in G. foliosus the abaxial anchor groups are so wide as to form an almost continuous abaxial layer).

Phytochemistry. Leaves without flavonoid sulphates (2 species).

Cytology. Chromosome base number, x = 10.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Gymnopogoninae. 15 species.

Distribution, phytogeography, ecology. America, West Indies.

Xerophytic; shade species and species of open habitats. Open places or light woodland on dry sandy soil.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia boutelouae.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - G. foliosus (Willd.) Nees.

Special comments. Lacking reliable data on ligule form, spikelet orientation, lemma form, number of stigmas, etc. Fruit data somewhat wanting.

Illustrations. • Gymnopogon foliosus, as Chloris: Kunth (1835). • Gymnopogon ambiguus, as G. racemosus: P. Beauv. (1812). • Gymnopogon ambiguus: Hitchcock and Chase (1950).

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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