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The grass genera of the world

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

Coelorachis Brongn.

From the Greek koilon (cavity) and rachis (axis), re swollen and hollowed rachides.

~ Mnesithea sensu lato

Including Apogonia Nutt, Coelorhachis Brongn., Cycloteria Stapf

Habit, vegetative morphology. Perennial (mostly), or annual (C. clarkei); mostly robust, tall, forming clumps. Culms 70–400 cm high; herbaceous; branched above, or unbranched above. Culm nodes hairy, or glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades linear; broad to narrow; flat (or rarely filiform); without cross venation; persistent. Ligule a fringed membrane to 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 (usually), or all alike in sexuality (C. parodiana); hermaphrodite (rarely), or hermaphrodite and male-only, or hermaphrodite and sterile. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic, or homomorphic; in both homogamous and heterogamous combinations, or all in heterogamous combinations. Plants exposed-cleistogamous, or chasmogamous (?).

Inflorescence. Inflorescence of spicate main branches, or paniculate (of long-peduncled, spikelike dorsiventral ‘racemes’, solitary at culm or branchlet apices, often in ‘false panicles’). Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (the unit consisting of a ‘raceme’, its peduncle, the subtending leaf and the next internode (the peduncle of the unit)). Spikelet-bearing axes spikelike; solitary, or clustered (fascicled); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (concave, clavate, shorter than the sessile spikelet); with a basal callus-knob; appendaged, or not appendaged; disarticulating transversely; glabrous. Spikelets paired, or in triplets (sometimes, then two sessile/one pedicellate); secund (the rachis dorsiventral, the sessile members alternating in two rows on one side); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis (but closely contiguous). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets hermaphrodite (C. parodiana), or male-only, or sterile.

Female-sterile spikelets. The pedicelled spikelets vestigial to well developed, bisexual in C.parodiana. The lemmas awnless.

Female-fertile spikelets. Spikelets 3–4.5 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; hairless; glabrous; awnless; very dissimilar (the lower two-keeled and two-winged above, the upper 1-keeled and wingless). Lower glume two-keeled (the keels winged); convex on the back to flattened on the back; not pitted; relatively smooth, or lacunose with deep depressions, or rugose; 7 nerved. Upper glume 0–2 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate (usually). Palea of the proximal incomplete florets when present, reduced. The proximal incomplete florets sterile. The proximal lemmas awnless; 0 nerved, or 2 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas lanceolate; less firm than the glumes (hyaline); not becoming indurated; entire; pointed; awnless; hairless; non-carinate; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated (hyaline); 2-nerved, or nerveless. 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; compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (long rectangles); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 33–42 microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 4.4–7. Microhair apical cells 18–22.5 microns long. Microhair apical cell/total length ratio 0.5–0.64. Stomata common; 27–30 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; in cork/silica-cell pairs; not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans; associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Special diagnostic feature. Spikelets not arranged as in Manisuris (q.v.). The lower lemma unlike that of Ophiochloa (i.e., without a central hyaline portion bordered by well developed, conspicously ciliate and terminally setose nerves, and without a pair of hygroscopically active setae at the apex).

Cytology. Chromosome base number, x = 9. 2n = 18, 36, and 54. 2, 4, and 6 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. About 20 species.

Distribution, phytogeography, ecology. Mainly tropical.

Helophytic to mesophytic; species of open habitats; glycophytic. Grassland and savanna, often on damp soils.

References, etc. Leaf anatomical: this project.

Illustrations. • C. lepidura: Hook. Ic. Pl. 31 (1922). • C. rottboellioides: Gardner, 1952. • C. capensis: Gibbs Russell et al., 1990. • Inflorescence detail (C. rottboellioides). • Inflorescence detail (C. rottboellioides). • C. rottboellioides, abaxial epidermis of leaf blade: original


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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: 13th November 2017. delta-intkey.com/grass’.

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