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The grass genera of the world

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

Raddia Bertol.

Including Hellera Doell., Strephium Nees

Habit, vegetative morphology. Perennial; caespitose, or caespitose and rhizomatous. The flowering culms leafy. Culms 10–50 cm high; herbaceous; where recorded, unbranched above (or ‘nearly simple’). The branching simple. Plants unarmed. Leaves few, not basally aggregated; without auricular setae. Leaf blades lanceolate, or elliptic (apiculate); broad, or narrow; 4–12 mm wide (and 1–7 cm long); rounded at base; pseudopetiolate; cross veined; rolled in bud. Ligule obsolete or fimbriate.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets in different inflorescences (comprising lateral synflorescences of female racemes, and terminal male panicles). The spikelets overtly heteromorphic.

Inflorescence. Inflorescence indeterminate (a synflorescence); a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes paniculate; persistent. Spikelets not secund; pedicellate (the pedicels short, those of female spikelets longer and apically expanded).

Female-sterile spikelets. Male spikelets shorter-pedicelled, florets with 2–3 free stamens. The male spikelets without glumes; 1 floreted. Male florets 2 staminate, or 3 staminate.

Female-fertile spikelets. Spikelets 7–8 mm long; elliptic, or ovate; compressed dorsiventrally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; free; pointed (acuminate); similar (firmly membranous, with cartilaginous, undulating margins, cf. Sucrea). Lower glume 5 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas gibbous; decidedly firmer than the glumes (leathery); becoming indurated; awnless, or mucronate (?); non-carinate; 5 nerved. Palea present; awnless, without apical setae; indurated; obscurely 2-nerved. Stamens 0.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but enclosed); small, or medium sized (2–7 mm long).

Seedling with a short mesocotyl. First seedling leaf without a lamina (or the blade much reduced).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae not over-arching the stomata; several per cell (small, thick-walled). Long-cells markedly different in shape costally and intercostally (costals much narrower); of similar wall thickness costally and intercostally (medium thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (45–)49–54(–57) microns long; (3.4–)4.5–5.4(–6) microns wide at the septum. Microhair total length/width at septum 9.2–11.5. Microhair apical cells 18–22.5 microns long. Microhair apical cell/total length ratio 0.38–0.42. Stomata common; 18–19.5–21 microns long. Subsidiaries predominantly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Costal short-cells conspicuously in long rows. Costal silica bodies oryzoid (predominating), or ‘panicoid-type’ (a few of the oryzoid form more or less isodiametric); when isodiametric, cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade; with arm cells (very conspicuous); with fusoids (very long and thin). The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a large median with a smaller lateral on each side). Bulliforms present in discrete, regular adaxial groups (these large, wide); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (with most bundles). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 11. 2n = 22. 2 ploid.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 5 species.

Distribution, phytogeography, ecology. Central and South America, West Indies.

Shade species.

References, etc. Morphological/taxonomic: Soderstrom and Zuloaga 1988. Leaf anatomical: studied by us - R. brasiliensis A. Bertoloni.

Special comments. Fruit data wanting. Illustrations. • R. guianensis: Hitchcock (1936)

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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: 11th December 2017.’.