Grass Genera of the World

L. Watson and M. J. Dallwitz


Rhomboelytrum Link

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; without cross venation; persistent; an unfringed membrane.

Reproductive organization. Plants bisexual, 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 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.).

Taxonomy. Pooideae; Poodae; Poeae.

Distribution, ecology, phytogeography. 2 species; South America. Species of open habitats. Stony slopes.

Neotropical and Antarctic. Andean. Patagonian.

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


Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).

Index