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The grass genera of the world

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

Chionachne R.Br.

From the Greek ciwn (snow) and achne (chaff), supposedly an allusion to pale-coloured glumes.

Habit, vegetative morphology. Annual (rarely), or perennial (reed-like); rhizomatous, or caespitose. Culms 60–200 cm high (?); woody and persistent, or herbaceous; sparsely or amply branched above, or unbranched above. The branching dendroid. Culm nodes hairy, or glabrous. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades broad; not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane to a fringed membrane (ciliate).

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets segregated, in different parts of the same inflorescence branch (female spikelets few, near the bases of the spikes, the male spikelets distal). The spikelets in both homogamous and heterogamous combinations (heterogamous below, male above).

Inflorescence. Inflorescence leafy, paniculate; open. Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’ to spikelike; solitary, or paired, or clustered; with substantial rachides; disarticulating; disarticulating at the joints. Spikelets solitary, or paired; secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis, or free of the rachis. The ‘shorter’ spikelets female-only (towards bases of spikes), or male-only (in the upper parts of the spikes, where they are paired with pedicellate male spikelets). The ‘longer’ spikelets male-only (above), or sterile (below, where they are reduced to pedicels, more or less fused with the rachis and paired with female sessile spikelets).

Female-sterile spikelets. Male spikelets solitary and sessile, or in pairs with one sessile and one pedicelled.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret.

Glumes two; very unequal; (the longer) long relative to the adjacent lemmas; awnless; very dissimilar (lower bigger, tough, rounded, with wings clasping the spikelet, the upper smaller, not tough, flat). Lower glume 7–20 nerved. Upper glume 7–9 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; sterile. The proximal lemmas awnless; 3 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; awnless; hairless; non-carinate; 1–5 nerved. Palea present; relatively long; 2-nerved. Lodicules absent. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 54–57 microns long; 9–12 microns wide at the septum. Microhair total length/width at septum 4.75–6. Microhair apical cells 30–33 microns long. Microhair apical cell/total length ratio 0.53–0.61. Stomata common; 42–48 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows, or predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib not readily distinguishable; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Maydeae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Chionachninae. 7 species.

Distribution, phytogeography, ecology. Indomalayan region, Indochina, eastern Australia.

Helophytic to mesophytic. Forest margins, streamsides.

Economic aspects. Significant weed species: C. hubbardiana (in North America). Cultivated fodder: C. semiteres.

Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: studied by us - C. cyathopoda (Muell.) Muell. ex Benth.

Illustrations. • C. cyathopoda: Gardner (1952). • C. cyathopoda, 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.’.