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The grass genera of the world

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

Cymbopogon Spreng.

From the Greek kumbe (boat) and pogon (beard), referring to many-awned inflorescences and boatshaped spathes.

Including Cymbanthelia Anderss., Gymnanthelia Schweinf.

Habit, vegetative morphology. Usually perennial (rarely annual); caespitose, or rhizomatous and caespitose. Culms 15–300 cm high; herbaceous; usually unbranched above. Culm nodes glabrous. Culm internodes solid. The shoots aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear (from broadly so to filiform); broad, or narrow; cordate, or not cordate, not sagittate; setaceous, or not setaceous; flat, or folded; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane to a fringed membrane. Contra-ligule absent.

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 (usually), or hermaphrodite and sterile; overtly heteromorphic (the pedicelled spikelets not depressed abaxially, awnless); in both homogamous and heterogamous combinations (the lowermost pair of the lowest raceme, or of each raceme, homogamous and imperfect). Plants outbreeding.

Inflorescence. Inflorescence paniculate (decompound, leafy). Rachides hollowed, or flattened, or winged, or neither flattened nor hollowed, not winged. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’ (short, spikelike, each pair with a spatheole); paired (the raceme bases short to more or less connate, flattened, often widely spreading or deflexed); with very slender rachides; disarticulating; disarticulating at the joints. ‘Articles’ linear; appendaged, or not appendaged; densely long-hairy to somewhat hairy. Spikelets paired (or with a terminal triplet); not secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis, or discernible, but fused with the rachis and free of the rachis (sometimes the pedicel of the homogamous pair being swollen and more or less fused with the internode). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only (usually), or sterile.

Female-sterile spikelets. Pedicellate spikelets never depressed or canaliculate on the back; only the L1 present, hyaline, 2-nerved, its floret usually male but occasionally sterile or suppressed. The male spikelets 1 floreted. The lemmas awnless.

Female-fertile spikelets. Spikelets 3–7 mm long; compressed laterally, or not noticeably compressed, or compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt.

Glumes two; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (the lower bicarinate, the upper naviculate). Lower glume two-keeled (the keels sometimes winged apically); flattened on the back to sulcate on the back; not pitted; relatively smooth; 1–5 nerved. Upper glume 1–5 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; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas; not becoming indurated (hyaline).

Female-fertile florets 1. Lemmas hyaline to firm-stipitate beneath the awn; less firm than the glumes; not becoming indurated; apically incised; 2 lobed; awnless, or awned. Awns when present, 1; from a sinus; geniculate; hairless (glabrous); 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 absent. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally (subterete to planoconvex). Hilum short. Embryo large; waisted. Endosperm hard; without lipid; containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–30 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (rarely), or absent. Intercostal papillae when present, consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally (narrow); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (long); having markedly sinuous walls, or having straight or only gently undulating walls (rarely). Microhairs present; panicoid-type, or chloridoid-type (rarely); (26–)30–48(–60) microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 4.8–7. Microhair apical cells (3–)13–22(–24) microns long. Microhair apical cell/total length ratio (0.17–)0.33–0.48–0.48. Stomata common; 21–22.5(–24) microns long. Subsidiaries variously low or high dome-shaped, or triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs (and solitary); not silicified (usually), or silicified. Intercostal silica bodies when present, tall-and-narrow, or cross-shaped, or vertically elongated-nodular. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular (occasionally).

Transverse section of leaf blade, physiology. C4; biochemical type NADP–ME (C. citratus); XyMS–. PCR sheath outlines uneven. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially (the colourless tissue often extending across the adaxial part of the blade). Bulliforms not present in discrete, regular adaxial groups (in irregular groups); occasionally, irregularly associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves containing flavonoid sulphates (1 species), or without flavonoid sulphates (4 species). Leaf blade chlorophyll a:b ratio 3.92–5.26.

Cytology. Chromosome base number, x = 5, or 10. 2n = 20, 22, 40, and 60.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. About 40 species.

Distribution, phytogeography, ecology. Tropical and subtropical Africa and Asia, Australia.

Mesophytic to xerophytic; species of open habitats; glycophytic. Savanna.

Economic aspects. Commercial essential oils: C. nardus and C. winterianus (citronella oil), C. flexuosus (East Indian Lemon-grass), C. citratus (West Indian Lemon-grass), C.martinii. C. citratus used as a culinary herb.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia nakanishikii, Puccinia eritraeensis, ‘Uromycesschoenanthi, Puccinia versicolor, and ‘Uromycesclignyi. Smuts from Ustilaginaceae. Ustilaginaceae — C. refractus.

References, etc. Morphological/taxonomic: Soenarko 1977. Leaf anatomical: Metcalfe 1960; studied by us - C. refractus (R. Br.) Camus.

Illustrations. • C. citratus: Hook. Ic. Pl. 29 (1907). • C. procerus: Gardner, 1952. • C. excavatus: Gibbs Russell et al., 1990. • Inflorescence (C. exaltatus). Cymbopogon exaltatus. Spatheate and spatheolate panicle, spikelet-bearing axes (‘racemes’) paired. • C. nardus, as Andropogon nardus var. validus: Wood, Natal Plants 2 (1904). • Inflorescence detail (C. procerus). • Inflorescence. • Pair of ‘racemes’ (C. ambiguus). • Inflorescence detail (C. refractus). Cymbopogon refractus. Pair of deflexed spikelet-bearing axes, showing their appendaged first joint. The one at the right bears a male spikelet to the left, and the axis continues on the right. • C. refractus, T.S. leaf blade: this project

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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.’.