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The grass genera of the world

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

Brachiaria (Trin.) Griseb.

From the Latin brachium (arm), alluding to the manner of bearing the racemes.

~ Urochloa

Type species: Type: B. eruciformis (Sm.) Griseb.

Habit, vegetative morphology. Annual (mostly), or perennial (sometimes in B. schoenfelderi); stoloniferous, or caespitose, or decumbent. Culms (10–)25–100 cm high; herbaceous; branched above, or unbranched above. The branching suffrutescent (e.g., B. fruticulosa), or simple (usually), or fastigiate (e.g., B. ambigens). Culms 3–6 noded. Culm nodes hairy. Culm leaf sheaths rounded. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear to lanceolate; narrow; 3–8(–11) mm wide (and 2–15(-18) cm long); flat, or rolled; without cross venation; persistent; rolled in bud. Ligule a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding (?). Apomictic, or reproducing sexually (?).

Inflorescence. Inflorescence of spicate main branches, or paniculate (the basal ‘racemes’ sometimes with secondary racemelets). Primary inflorescence branches 4–17 (?); borne biseriately on one side of the main axis. Inflorescence with axes ending in spikelets. Rachides hollowed (or triquetrous), or winged. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate; pedicellate (the pedicels 0.2–0.5 mm long). Pedicel apices concave, discoid. Spikelets imbricate; not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets 1.6–3.7 mm long; broadly elliptic; adaxial; compressed dorsiventrally; biconvex; primarily disarticulating above the glumes (at the base of the upper floret, but with a secondary disarticulation beneath the glumes); disarticulating between the florets (this distinguishing Brachiaria sensu stricto from Urochloa sensu lato). Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes two; very unequal (the lower a small scale); long relative to the adjacent lemmas (i.e. the upper glumes); dorsiventral to the rachis; hairy, or hairless, or hairy and hairless (the lower usually glabrous); awnless; non-carinate; very dissimilar (the lower much reduced, the upper similar to the L1). Lower glume 0–1 nerved. Upper glume 3–5 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. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male, or sterile. The proximal lemmas awnless (muticous); 3–5(–7) nerved (the laterals distant from the median); more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas; not becoming indurated (membranous).

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (chartaceous to cartilaginous); smooth (and shiny); becoming indurated to not becoming indurated; white in fruit; entire; blunt; not crested; awnless; hairless; glabrous; non-carinate; having the margins inrolled against the palea; with a clear germination flap; obscurely 3–5 nerved. Palea present (the tip not reflexed); relatively long; tightly clasped by the lemma; entire (apically rounded); awnless, without apical setae; textured like the lemma; indurated; 2-nerved. 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 small; compressed dorsiventrally. Hilum short. Embryo large. Endosperm hard; without lipid. 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 (rarely), or absent (?). Intercostal papillae not over-arching the stomata. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (32–)40–67(–76) microns long (?). Microhair apical cells (18–)26–48 microns long (?). Microhair apical cell/total length ratio 0.52–0.69 (?). Stomata common. Subsidiaries dome-shaped, or triangular (?). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare (?); in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular (?).

Transverse section of leaf blade, physiology. C4; biochemical type PCK; XyMS+. PCR sheath outlines uneven. PCR sheath extensions present, or absent (?). Maximum number of extension cells if present, 1. PCR cells with a suberised lamella. PCR cell chloroplasts ovoid; with well developed grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section to adaxially flat (?). Midrib conspicuous, or not readily distinguishable (?); with one bundle only, or having a conventional arc of bundles (?); without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans, or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (?). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent (?); nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (?).

Cytology. Chromosome base number, x = 9. 2n = 18. 2 ploid. Chromosomes ‘small’. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melidininae. 3 species (B. eruciformis, B. malacodes, B. schoenfelderi).

Distribution, phytogeography, ecology. Africa and Mediterranean.

Commonly adventive (notably B. eruciformis). Mesophytic; shade species, or species of open habitats; glycophytic.

Economic aspects. Significant weed species: B. eruciformis.

Rusts and smuts. Rusts — Physopella and Puccinia. Taxonomically wide-ranging species: Puccinia orientalis, Puccinia levis, and ‘Uromycessetariae-italicae. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Melanotaenium and Tilletia. Ustilaginaceae — Sorosporium, Sphacelotheca, Tolyposporella, and Ustilago.

References, etc. Morphological/taxonomic: Webster (1987), Morrone and Zuloaga (1992 and 1993), Veldkamp (1996). Leaf anatomical: Metcalfe 1960; studied by us - B. eruciformis (J.E. Sm.) Griseb.

Special comments. For justification of this sensu stricto interpretation, see Webster (1987), Morrone and Zuloaga (1992), and Veldkamp (1996). In Watson’s opinion, however, it would have been better to delay such realignments until generic circumscriptions around Panicum had been broadly reassessed on a basis of worldwide sampling. Illustrations. • B. ramosa, as Panicum arvense: Kunth (1835). • B. eruciformis: Fl. Iraq, 1968. • B. eruciforms, abaxial epidermis of leaf blade: this project

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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: 11th December 2017.’.