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The grass genera of the world

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

Rhomboelytrum Link

~ Chascolytrum

Including Rhombolytrum Link

Excluding Gymnachne

Habit, vegetative morphology. Perennial; rhizomatous, or caespitose. Culms about 10–50 cm high; herbaceous; unbranched above. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; flat, or rolled; not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane.

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

Inflorescence. Inflorescence paniculate; contracted; spicate to more or less irregular; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate; imbricate.

Female-fertile spikelets. Spikelets 4.5–7 mm long; rhomboidal or oblong; compressed laterally (but the florets dorsiventrally flattened); disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present. Callus short.

Glumes two; more or less equal; shorter than the spikelets; long relative to the adjacent lemmas; hairless; scabrous; awnless; carinate (the keel scabrid); similar (lanceolate or naviculate). Lower glume about equalling the lowest lemma; 3 nerved, or 5 nerved. Upper glume 3 nerved, or 5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless. Spikelets without proximal incomplete florets.

Female-fertile florets 4–10. Lemmas broadly lanceolate or rhomboid, with thickened margins in the lower third; becoming indurated (on the lower third of the margins, thin towards the tip); entire, or incised; pointed; when incised, 2 lobed; when incised, not deeply cleft (bidentate); awnless to mucronate; hairy (especially on the margins below); non-carinate; without a germination flap; 5 nerved, or 7 nerved, or 9 nerved. Palea present; relatively long (lanceolate); tightly clasped by the lemma; entire to apically notched; awnless, without apical setae; thinner than the lemma (papery); not indurated; 2-nerved; 2-keeled (flat between the hairy or fringed keels). Palea keels slightly winged; hairy. Lodicules present; 2; free; membranous; glabrous; not toothed. Stamens 1. Anthers very small in cleistogamous florets. Ovary apically glabrous. Styles free to their bases (subsessile). Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea (to the palea); small; ellipsoid; compressed dorsiventrally. Hilum short. Embryo small. Endosperm hard.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrow, rectangular); of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells mostly fusiform; having markedly sinuous walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided to triangular (many approaching the ‘triangular with truncated apices’ configuration). Guard-cells overlapped by the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly in short rows to paired). Costal silica bodies horizontally-elongated crenate/sinuous (a few, but short and irregular so as sometimes to approach panicoid type crosses etc.), or rounded (a few, variously distorted), or crescentic (common, but variously distorted), or ‘panicoid-type’ (a few); a few assignable as cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size (mostly round topped). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (a large group in each furrow); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (slender to heavy I’s). Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Lemmas not as in Briza (q.v.).

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Calothecinae. 2 species.

Distribution, phytogeography, ecology. South America.

Species of open habitats. Stony slopes.

References, etc. Morphological/taxonomic: Nicora and Rúgolo de Agrasar 1981. Leaf anatomical: this project.

Illustrations. • R. rhomboideum: Nicora & Rúgolo de Agrasar (1987)


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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