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The grass genera of the world

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

Coelachne R.Br.

From the Greek koilos (hollow) and achne (chaff, scale), referring to a ventricose lower lemma.

Type species: Type: C. pulchella R.Br.

Habit, vegetative morphology. Low annual, or perennial; caespitose, or decumbent. Culms 4–50 cm high; herbaceous. Culm nodes glabrous. Culm leaf sheaths rounded. Leaves non-auriculate. Leaf blades linear to ovate-lanceolate; narrow; not pseudopetiolate; cross veined, or without cross venation; persistent; rolled in bud. Ligule a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence of spicate main branches, or paniculate; open, or contracted; with capillary branchlets, or without capillary branchlets. Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; not secund; pedicellate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets ovate; not noticeably compressed to compressed dorsiventrally; disarticulating above the glumes; disarticulating between the florets; with distinctly elongated rachilla internodes between the florets. Rachilla terminated by a female-fertile floret; hairy. Hairy callus present, or absent.

Glumes two (persistent); very unequal to more or less equal; shorter than the spikelets (1/3 to 2/3 their length); shorter than the adjacent lemmas; hairless (usually glabrous); not pointed (obtuse); awnless; non-carinate; similar (broad, membranous). Lower glume 1–5 nerved. Upper glume 3–7 nerved. Spikelets with female-fertile florets only (but the upper floret female-only); without proximal incomplete florets.

Female-fertile florets 2 (these dissimilar, separated by a slender rachilla segment). Lemmas saccate (sometimes, the lower), or not saccate; decidedly firmer than the glumes (the lower becoming somewhat hardened, the upper remaining membranous); smooth; not becoming indurated; white in fruit; entire; blunt; awnless (obtuse); hairy (L2 usually pubescent), or hairless (L1 basally hairy or not); non-carinate; with a clear germination flap; 0 nerved. Palea present; entire (obtuse); awnless, without apical setae; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 2–3. Anthers not penicillate. Ovary apically glabrous. Styles fused, or free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Embryo large, or small; not waisted. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent. Intercostal papillae over-arching the stomata, or not over-arching the stomata; consisting of one symmetrical projection per cell (but not on every cell). Long-cells markedly different in shape costally and intercostally (the costals short, irregularly shaped); of similar wall thickness costally and intercostally (thin walled). Intercostal zones without typical long-cells (the cells mainly more or less isodiametric). Mid-intercostal long-cells rectangular (hexagonal to square); having straight or only gently undulating walls. Microhairs present; more or less spherical, or elongated; ostensibly one-celled, or clearly two-celled; chloridoid-type (apical cell somewhat pointed, but thick walled and broader than long); (7–)13–38(–42) microns long. Microhair apical cells 7–24(–26) microns long. Microhair apical cell/total length ratio 0.64–0.73. Stomata common; 24–27 microns long. Subsidiaries parallel-sided to triangular; including both triangular and parallel-sided forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; not paired; not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies acutely-angled (more or less cubical); sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; Isachne-type. 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. Bulliforms present in discrete, regular adaxial groups (in the furrows, the groups sometimes inconspicuous); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10. 2n = 40.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Isachneae. Soreng et al. (2015): Micrairoideae; Isachneae. 10 species.

Distribution, phytogeography, ecology. Palaeotropical.

Helophytic; species of open habitats; glycophytic. Streamsides and marshes.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - C. pulchella R. Br.

Illustrations. • C. pulchella: Kunth (1835). • C. pulchella, abaxial epidermis of leaf blade: this project. • C. pulchella, 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: 11th December 2017.’.