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The grass genera of the world

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

Brachyachne (Benth.) Stapf

From the Greek brachys (short) and achne (scale, chaff), alluding to lemmas shorter than glumes.

Native Couch.

~ Cynodon

Type species: Type: B. convergens (F. Muell.) Stapf; lecto, fide C.E. Hubbard, Hooker’s Icon. Pl. t. 3362 (1938).

Excluding Lepturidium

Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms 8–70 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid. Leaves non-auriculate. Leaf blades linear; narrow; setaceous, or not setaceous; flat, or rolled (involute and filiform); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane to a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence usually of spicate main branches (occasionally the racemes single); digitate. Inflorescence with axes ending in spikelets. Rachides hollowed, or flattened (or triquetrous). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary (appressed); secund (the racemes unilateral); biseriate; subsessile.

Female-fertile spikelets. Spikelets adaxial; strongly compressed laterally; disarticulating above the glumes. Rachilla usually prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets, or naked. Hairy callus present. Callus short; pointed, or blunt.

Glumes two; more or less equal; exceeding the spikelets (enclosing the floret); long relative to the adjacent lemmas; lateral to the rachis; pointed, or not pointed (sometimes minutely incised, with a tiny mucro); awnless; (at least the lower) carinate (the keel weak to very strong); with the keel conspicuously winged (especially the lower, in B. convergens), or without a median keel-wing; very dissimilar (broad, usually thinly leathery, the lower curved in profile, the upper straighter). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped (tiny). Spikelets without proximal incomplete florets.

Female-fertile florets 1. Lemmas less firm than the glumes to similar in texture to the glumes (membranous to hyaline); not becoming indurated; entire, or incised; when entire, pointed, or blunt; when incised, 2 lobed; not deeply cleft; awnless, or mucronate (rarely); hairy (long-haired on the nerves or all over); carinate (folded along the mid-nerve); 3 nerved. Palea present; relatively long to conspicuous but relatively short; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (with long hairs). Lodicules present; 2; joined, or free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; not waisted. Endosperm containing compound starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae not over-arching the stomata; consisting of one symmetrical projection per cell. Long-cells the intercostals broader, often short; of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells, or exhibiting many atypical long-cells. Mid-intercostal long-cells rectangular (to square); having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 6 microns long. Stomata common. Subsidiaries non-papillate. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (mainly solitary); silicified (mostly), or not silicified (usually). Intercostal silica bodies imperfectly developed; tall-and-narrow (rare). Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral, or centripetal. Mesophyll with radiate chlorenchyma. Leaf blade ‘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. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 10 species.

Distribution, phytogeography, ecology. Africa, Australia.

Helophytic to mesophytic; species of open habitats; glycophytic. Seasonal swamps and moist rock crevices.

Economic aspects. Significant weed species: B. convergens (in North America).

References, etc. Leaf anatomical: studied by us - B. convergens (F. Muell.) Stapf.

Illustrations. • B. tenella, as Cynodon: Kunth (1835). • B. fulva: Hook. Ic. Pl. 31 (1922). • B. convergens: Gardner, 1952. • General aspect (B. convergens, B. ciliaris). • Spikelet of B. convergens. • B. convergens, abaxial epidermis of leaf blade - general view: this project. • B. convergens, abaxial epidermis of leaf blade - details. • B. convergens, abaxial epidermis of leaf blade - details

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.’.