| # 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. The shoots not aromatic. 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. 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: studied by us - C. rottboellioides (R. Br.) Camus.

Illustrations. • Coelorachis lepidura: Hook. Ic. Pl. 31 (1922). • Coelorachis rottboellioides: Gardner, 1952. • Coelorachis capensis: Gibbs Russell et al., 1990. • Inflorescence detail (C. rottboellioides). • Inflorescence detail (C. rottboellioides). • Coelorachis rottboellioides, 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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