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The grass genera of the world

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

Urochloa P. Beauv.

Type species: Type: U. panicoides P.Beauv.

Including Moorochloa (= U. mosambicensis, Pseodobrachiaria

Excluding Brachiaria

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms (7–)20–200 cm high; herbaceous; branched above, or unbranched above; tuberous, or not tuberous. Culm nodes hairy, or glabrous. Culm leaf sheaths keeled (mostly), or rounded. Culm internodes solid, or hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear, or linear-lanceolate, or lanceolate, or ovate-lanceolate; broad, or narrow; 2.6–20 mm wide; not cordate, not sagittate; flat, or folded, or rolled; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule present, or absent (rarely); an unfringed membrane (rarely), or a fringed membrane, or a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (then some spikelets reduced to disc-tipped pedicels), or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile. Plants outbreeding. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence of spicate main branches; digitate, or subdigitate, or non-digitate. Primary inflorescence branches (1–)2–30; borne biseriately on one side of the main axis, or inserted all around the main axis. Inflorescence with axes ending in spikelets (nearly always), or axes not ending in spikelets (or at least with only rudimentary terminal spikelets, e.g. U. ruziziensis). Rachides hollowed, or flattened, or winged, or neither flattened nor hollowed, not winged (filiform to triquetrous of ribbonlike). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; solitary, or paired (occasionally in fascicles); secund; biseriate (on one side of the rachis); sessile, or subsessile, or pedicellate. Pedicel apices oblique, or discoid. Spikelets not in distinct ‘long-and-short’ combinations.

Female-sterile spikelets. The staminal filaments of female-sterile spikelets free.

Female-fertile spikelets. Spikelets oblong, or elliptic, or lanceolate, or ovate, or obovate, or oblanceolate; abaxial (Urochloa sensu stricto), or adaxial (Brachiaria sensu lato, and generally when the spikelets are paired), or abaxial to adaxial (the orientation being not infrequently ambiguous); not noticeably compressed, or compressed dorsiventrally; planoconvex, or biconvex; falling with the glumes; not disarticulating between the florets; with conventional internode spacings, or with a distinctly elongated rachilla internode between the glumes (the internode then often accrescent to the sheathing base of the lower glume). Rachilla prolonged beyond the uppermost female-fertile floret (occasionally), or terminated by a female-fertile floret; the rachilla extension when present, naked. Callus absent, or short (if a short stipe representing accrescence of the base of G1 and the internode above is seen as ‘callus’).

Glumes two; very unequal, or more or less equal; long relative to the adjacent lemmas (i.e. the longer, upper glumes); dorsiventral to the rachis (or their orientation ambiguous); hairy, or hairless; awnless; very dissimilar, or similar. Lower glume 0 nerved, or 1–2 nerved, or 3–7(–11) nerved (e.g. U. jubata, with 7–11). Upper glume 5–11 nerved. Spikelets nearly always with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets nearly always with proximal incomplete florets. The proximal incomplete florets 1; paleate (usually), or epaleate. Palea of the proximal incomplete florets fully developed, or reduced. The proximal incomplete florets male (occasionally even bisexual), or sterile. The proximal lemmas awnless (muticous); 5–7 nerved (and sometimes cross-veined); more or less equalling the female-fertile lemmas, or decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas; becoming indurated (very rarely), or not becoming indurated.

Female-fertile florets nearly always only 1. Lemmas decidedly firmer than the glumes; striate, or rugose (i.e. usually more or less sculptured and dull); becoming indurated, or not becoming indurated (leathery, cartilaginous or crustaceous); white in fruit, or yellow in fruit; entire; pointed, or blunt; crested at the tip (rarely, e.g. U. paucispicata), or not crested (usually); awnless, or mucronate, or awned (i.e. muticous to shortly awned, ‘mucronate to awned’ condition having previously been used to distinguish Urochloa sensu stricto from Brachiaria sensu lato). Awns when detectable, 1; median; apical; non-geniculate; hairless; much shorter than the body of the lemma. Lemmas hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 3–4 nerved, or 5 nerved, or 6–7 nerved. Palea present; relatively long; gaping (sometimes?), or tightly clasped by the lemma; entire; awnless, without apical setae; thinner than the lemma, or textured like the lemma (?); indurated, or not indurated (?); 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3; with free filaments. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit small; ellipsoid, or subglobose; compressed dorsiventrally. Hilum short. Pericarp thin. Embryo large; waisted. Endosperm hard; without lipid; containing only simple starch grains. Embryo (recorded only for Brachiaria sensu lato) without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present, or absent. Intercostal papillae not over-arching the stomata. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 32–76 microns long; 4.5–6 microns wide at the septum. Microhair total length/width at septum 12.5–16.7. Microhair apical cells 18–48 microns long. Microhair apical cell/total length ratio 0.52–0.69. Stomata common; 31.5–33 microns long. Subsidiaries dome-shaped, or triangular; not including both parallel-sided and triangular forms on the same leaf. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; in cork/silica-cell pairs, or not paired; silicified, or not silicified. Intercostal silica bodies when present, cross-shaped, or vertically elongated-nodular. Crown cells absent. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4. The anatomical organization conventional. Biochemical type PCK; XyMS+. PCR sheath outlines uneven. PCR sheath extensions present, or absent. Maximum number of extension cells when 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, or adaxially flat; when ribbed, with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates. Leaf blade chlorophyll a:b ratio of Pseudobrachiaria = U. deflexa 3.36–3.43.

Special diagnostic feature. No Eriochloa-type ‘callus’.

Cytology. Chromosome base number, x = 7 and 9. 2n = 18, 28, 32, 36, 48, 54, 64, and 72. Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melidininae. About 120 species.

Distribution, phytogeography, ecology. Pantropical.

Commonly adventive. Helophytic, or mesophytic, or xerophytic; shade species and species of open habitats; glycophytic.

Economic aspects. Significant weed species: U. ciliatissima, U. deflexa, U. distachya, U. fasciculata, U. lata, U. mutica, U. paspaloides, U. plantaginea, U. platyphylla, U. ramosa, U. reptans, U. texana. Cultivated fodder: U. arrecta (Tanner), U. brizantha (Palisade), U. decumbens (Surinam), U. mutica (Para). Important native pasture species: U. brizantha, U. bovonei, U. comata, U. decumbens, U. deflexa, U. distachya, U. jubata, U. nigropedata, U. serrata etc. Grain crop species: U. deflexa - a minor cereal in West Africa.

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 - U. decumbens (Stapf) Webster, U. foliosa (R.Br.) Webster, U. mosambicensis (Hackel) Dandy.

Special comments. For justification of this sensu lato treatment of Urochloa, see taxonomic comments under Brachiaria. Illustrations. • U. panicoides: P. Beauv. (1812). • U. (Brachiaria) gilesii: Gardner, 1952. • General aspect (U. mosambicensis): Gibbs Russell et al., 1990. • General aspect (U. serrata): Gibbs Russell et al., 1990. • General aspect (U. deflexa): Gibbs Russell et al., 1990. • Inflorescence of U. aff. foliosa. • Inflorescence detail. • Inflorescence detail of U. decumbens. • Rachis detail of U. decumbens. • U. decumbens, abaxial epidermis of leaf blade: this project. • U. foliosa, T.S. leaf blade with fluorescent-labelled Rubisco: Hattersley. Urochloa foliosa. Fluorescent-labelled Rubisco in the PCR sheath. • U. decumbens, TS 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.’.