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The grass genera of the world

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

Chrysopogon Trin.

From the Greek chrysos (golden) and pogon (beard), alluding to golden brown callus hairs of some species.

Including Centrophorum Trin., Chalcoelytrum Lunell, Pollinia Spreng., Raphis Lour., Trianthium Desv.

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 15–150 cm high; herbaceous; branched above, or unbranched above. The branching simple, or fastigiate. Culm nodes hairy, or glabrous. Culm internodes solid. Leaves mostly basal; non-auriculate. Leaf blades narrow (often harsh and glaucous); without cross venation; persistent. Ligule a fringed membrane (short), or a fringe of hairs.

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; overtly heteromorphic (pedicellate spikelets flattened dorsally, awnless or not, often purple, the sessile spikelet often pallid or yellowish); all in heterogamous combinations.

Inflorescence. Inflorescence paniculate (the branches usually with terminal triads of spikelets, but sometimes with a long-pedicel/short-pedicel pair below the triad); open (with whorls of slender, persistent branches); with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (usually to a single joint and the terminal triad, but sometimes with a long-pedicel/short-pedicel pair below); with very slender rachides; disarticulating; disarticulating at the joints (beneath the triad, and beneath the pairs when present). ‘Articles’ without a basal callus-knob; disarticulating obliquely. Spikelets in triplets, or in triplets and paired; not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile (with flat pedicels).

Female-sterile spikelets. Male spikelets often purplish, on slender pedicels, dorsally compressed, awned or awnless, L1 empty, L2 with a male floret. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; with proximal incomplete florets; 2 floreted. The lemmas awnless, or awned. Male florets 1.

Female-fertile spikelets. Spikelets 5–8.5 mm long; compressed laterally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. The callus hairs brown (commonly fulvous), or white (?).

Glumes two; more or less equal; long relative to the adjacent lemmas; awned and awnless (G2 often awned), or awnless. Lower glume two-keeled, or not two-keeled; convex on the back (or keeled upwards, sometimes with spinulose margins); not pitted; relatively smooth; 5–7 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire, or incised; when two-lobed not deeply cleft (bidentate); awned. Awns 1; median; from a sinus, or apical; geniculate; hairless (glabrous), or hairy; much shorter than the body of the lemma to much longer than the body of the lemma (?). Lemmas hairless; non-carinate; 1–3 nerved. Palea present, or absent; when present, conspicuous but relatively short, or very reduced; not indurated; nerveless. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; compressed laterally. Hilum short. Embryo large. Endosperm hard; without lipid.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (but the intercostals with somewhat rounded ends); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (with the ‘corners’ rounded); having markedly sinuous walls. Microhairs present; panicoid-type; (48–)50–60(–64) microns long. Microhair apical cells (25–)30–36 microns long. Microhair apical cell/total length ratio 0.6. Stomata common. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies crescentic and cross-shaped. Costal short-cells predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped, or dumb-bell shaped.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana (rudimentary); centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only (rarely), or having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups (or in more or less irregular groups), or not present in discrete, regular adaxial groups (sometimes the groups confined to midrib hinges); in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 5 and 10. 2n = 20 and 40. Chromosomes ‘small’.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 25 species.

Distribution, phytogeography, ecology. Tropical and subtropical.

Mesophytic, or xerophytic (from subdesert to rainforest); species of open habitats; glycophytic. On poor soils, often in disturbed ground.

Economic aspects. Significant weed species: C. aciculatus (sometimes, in pastures). Cultivated fodder: C. fulvus. Important native pasture species: C. plumulosus. Lawns and/or playing fields: C. aciculatus (in the humid tropics).

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - C. fallax Blake.

Illustrations. • C. aucheri: Fl. Iraq, 1968. • C. fallax: Gardner, 1952. • C. serrulatus: Gibbs Russell et al., 1990

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: 11th December 2017.’.