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The grass genera of the world

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

Rhynchoryza Baillon

Habit, vegetative morphology. Perennial. Culms herbaceous. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear; narrow; 5–10 mm wide; flat; seemingly pseudopetiolate (see illustration by Nicora and Rúgolo de Agrasar 1987); without cross venation; persistent. Ligule an unfringed membrane; not truncate (acute); large.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate; open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets unconventional (owing to extreme reduction of the glumes, cf. Oryza); about 15–25 mm long; lanceolate; compressed laterally; disarticulating above the glumes (in so far as these can be said to be present). Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes present to absent (vestigial, cf. Oryza); if considered present, two; minute; more or less equal; shorter than the spikelets; 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 (the lower larger); epaleate; sterile (much reduced, cf. Oryza). The proximal lemmas broadly ovate, cuspidate; awnless; 3 nerved; exceeded by the female-fertile lemmas (only about 1/10 the length of the spikelet); not becoming indurated.

Female-fertile florets 1. Lemmas leathery below, with the tip beneath the awn in the form of a beak extending beyond the palea, containing transversely septate aerenchyma and specialised as a flotation device; becoming indurated; entire; pointed; awned. Awns 1; apical; non-geniculate; hairless. Lemmas hairless; carinate; without a germination flap; 5 nerved. Palea present; relatively long; textured like the lemma; several nerved; one-keeled. Lodicules present; 2; membranous. Stamens 6. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit not noticeably compressed (‘cylindrical to somewhat hexagonal in section’). Hilum long-linear. Embryo small. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal (in the broad stomatal zones - adjoining the costae - only). Intercostal papillae over-arching the stomata (often from the interstomatals, as well as from the subsidiaries); several per cell (round, rather irregular in size and distribution on each cell). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; ostensibly one-celled; panicoid-type. Stomata common. Subsidiaries papillate; predominantly triangular. Intercostal short-cells common (especially in the astomatal regions); in cork/silica-cell pairs; silicified. Intercostal silica bodies narrowly oryzoid-type. Costal short-cells predominantly paired (and a few short rows). Costal silica bodies predominantly oryzoid (these abundant), or tall-and-narrow (a few, representing poorly developed oryzoids); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; with arm cells (conspicuous); with fusoids. The fusoids external to the PBS (these unusual, in that they are often in pairs contiguous on their long axes, and sometimes with a third contiguous member inside, projecting further into the intercostal region). Leaf blade adaxially flat. Midrib very conspicuous (being much enlarged and aerenchymatous, with conspicuous groups of stellate chlorenchyma); having complex vascularization (with a complete, peripheral ring of bundles, the adaxial series being smaller but not ‘inverted’, and with a few small ‘disorientated’ bundles in the internal trabeculae between the air cavities); with colourless mesophyll adaxially (and large lacunae). Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (most bundles with I’s). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Female-fertile lemma with its tip extended beyond the palea as a conical, herbaceous beak (flotation device) composed of aerenchyma with transverse septa, tapering into an awn.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Oryzeae. Soreng et al. (2015): Oryzoideae; Oryzeae; Zizaniinae. 1 species.

Distribution, phytogeography, ecology. Paraguay to Argentina.

Helophytic; glycophytic.

References, etc. Leaf anatomical: this project.

Illustrations. • R. subulata: Nicora & Rúgolo de Agrasar (1987). • R. subulata, 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: 13th November 2017. delta-intkey.com/grass’.

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