| # 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. • Raddia guianensis: Hitchcock (1936).

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: 15th June 2025. delta-intkey.com’.

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