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The grass genera of the world

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

Oryza L.

Latinized from the Arabic uruz (rice), whence Greek oruza is also derived.

Rice.

Type species: Type: O. sativa L.

Including Padia Moritzi

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or caespitose. Culms 30–300 cm high; herbaceous. Culm nodes glabrous. Culm internodes hollow. Leaves not basally aggregated; usually auriculate; with auricular setae (auricles with up to 4 setae), or without auricular setae. Leaf blades linear to linear-lanceolate; neither leathery nor flimsy; broad, or narrow; flat; pseudopetiolate, or not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane; 3–45 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants outbreeding and inbreeding; exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence paniculate (axes usually wavy, the spikelets appressed), or of spicate main branches (the primary branches often reduced to racemes); open; with capillary branchlets, or without capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets unconventional (disarticulating above a cupuliform pedicel apex, which is taken to represent glumes, so that the organ serving as a palea may ‘really’ be a lemma); 4–12 mm long; oblong, or elliptic, or ovate; strongly compressed laterally; disarticulating above the glumes (i.e. above the pedicel cup representing them); with conventional internode spacings (i.e. the floret not stipitate). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes present to absent (represented only by a small 2-lobed cupule); if present, two; minute; more or less equal; shorter than the adjacent lemmas; joined; awnless. Lower glume 0 nerved. Upper glume 0 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 2 (small, vestigial, no more than half the spikelet length, sometimes only bristles); epaleate; sterile. The proximal lemmas awnless; exceeded by the female-fertile lemmas (usually between 1/8 and 1/2 the length of the spikelet).

Female-fertile florets 1. Lemmas becoming indurated to not becoming indurated (leathery to indurated); entire; pointed; awnless, or mucronate, or awned. Awns when present, 1; apical; non-geniculate; much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairy (hispid-ciliate on the nerves), or hairless (glabrous); strongly carinate; without a germination flap; 3–9 nerved. Palea present; relatively long (but narrower than the lemma); tightly clasped by the lemma (along the lateral nerves); entire (mucronate to subulate); awnless, without apical setae, or with apical setae, or awned (sometimes with an apical awn or seta); textured like the lemma; not indurated (leathery); several nerved; one-keeled. Lodicules present; 2; membranous (but the membranous flange may be narrow); glabrous; toothed, or not toothed; heavily vascularized. Stamens 6. Anthers 2–3 mm long; not penicillate. Ovary apically glabrous. Styles fused (basally), or free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea, or free from both lemma and palea; small, or medium sized, or large; compressed laterally. Hilum long-linear. Embryo small. Endosperm hard; without lipid; containing compound starch grains. Embryo with an epiblast; with a scutellar tail to without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl. First seedling leaf without a lamina.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata (to some extent); several per cell (O. australiensis having long-cells variously with a single longitudinal row of large papillae, a double row of half-sized ones, or something in between; and the guard-cells over-arched at their ends by tiny projections, seemingly from the subsidiaries). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; without ‘partitioning membranes’ (in O. sativa); (24–)26–42(–45) microns long; 3.6–5.4 microns wide at the septum. Microhair total length/width at septum 7.1–12.5. Microhair apical cells (14–)19–22.5(–25.5) microns long. Microhair apical cell/total length ratio 0.46–0.57. Stomata common; (22.5–)24–28.5(–30) microns long. Subsidiaries papillate; dome-shaped, or triangular (mostly). Guard-cells overlapped by the interstomatals (very slightly). Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies oryzoid (mostly), or rounded, or crescentic (the rounded and crescentic forms associated with the short-cell pairs which occur over some veins in O. sativa); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; with arm cells; without fusoids. Leaf blade with the ribs more or less constant in size (except for enlarged ribs associated with the leaf margins), or with the ribs very irregular in sizes. Midrib conspicuous; having complex vascularization. Bulliforms present in discrete, regular adaxial groups; in simple fans, or in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans (a few Sporobolus-type groups in at least some species, e.g. O. australiensis). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (in most bundles). Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (2 species).

Special diagnostic feature. Not scandent as in Prosphytochloa (q.v.).

Cytology. Chromosome base number, x = 12. 2n = 24 and 48. 2 and 4 ploid. Chromosomes ‘small’. Haploid nuclear DNA content 0.6–1.1 pg (12 species, mean 0.8). Mean diploid 2c DNA value 1.7 pg (10 species, 1.1–2.5). Nucleoli persistent.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Oryzeae. Soreng et al. (2015): Oryzoideae; Oryzeae; Oryzinae. 25 species.

Distribution, phytogeography, ecology. Tropical.

Commonly adventive. Hydrophytic, or helophytic; shade species, or species of open habitats; glycophytic.

Economic aspects. Significant weed species: O. barthii, O. perennis (in rice), O. punctata, O. rufipogon. Important native pasture species: e.g. O. longistaminata(Kenya), O. ridleyi (Malaya). Grain crop species: O. sativa (Rice); also O. glaberrima (west Africa).

Hybrids. Intergeneric hybrid claimed with Triticum: ×Oryticum Wang & Tang in Acta Phytotax. Sin. 20, 179 (1982).

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia graminis. Smuts from Tilletiaceae. Tilletiaceae — Entyloma and Tilletia.

References, etc. Leaf anatomical: Metcalfe 1960; this project.

Illustrations. • General aspect (O. longistaminata): Gibbs Russell et al., 1990. • O. sativa: Lamson-Scribner (1890). • O. australiensis: Gardner, 1952. • Inflorescence and spikelet details of O. australiensis: this project. Oryza australiensis. Right, pedicels with minute glumes retained after spikelet abscission. Left, spikelet with minute glumes, two short, thin sterile lemmas (left and right), awned scabrous fertile lemma (right) and palea of similar texture (left). • O. australiensis, abaxial epidermis of leaf blade: this project. • O. australiensis, abaxial epidermis of leaf blade: this project. • General aspect (O. rufipogon): E. Hickman


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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: 13th November 2017. delta-intkey.com/grass’.

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