The genera of Leguminosae-Caesalpinioideae & Swartzieae
Type species: O. micranthum (Harms) Bak. f.
Habit and leaf form. Trees; unarmed.
Phyllotaxy distichous, or spiral. The leaves compound; pinnate, or bifoliolate; paripinnate (but with a rachis extension). The leaflets few per leaf; alternate; petiolulate; without noticeably twisted petiolules. Stipules present, persistent and conspicuous in mature leaves; membranous; connate (enclosing the buds). Stipels absent.
Inflorescence and floral morphology. The inflorescences axillary and terminal; branched; of racemose units (?); panicles. The flowers not distichous. Bracts small, caducous, absent at anthesis. Bracteoles present; sepaloid, concave, relatively large and enclosing the flower buds; persistent beyond anthesis; valvate.
The flowers hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx, or in the calyx and in the androecium (rarely). Hypanthium more or less absent, the androecium hypogynous. The perianth comprising distinct calyx and corolla. Calyx 4; covering the rest of the flower in bud; polysepalous; more or less regular (the sepals similar to one another); members imbricate. Corolla present; regular; 5; without greatly reduced members; polypetalous. Petals entire, equal and similar to one another, imbricate; imbricate-ascending. The androecium comprising 8–10 members; members all free of one another; members all more or less equal in length; comprising only fertile stamens. Fertile stamens (8–)10. Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary villous, stipitate; eccentric, with the stipe adnate (the style filiform). Ovules few (2–5).
Fruit, seed and seedling. Fruit a two-valved pod; valves twisting and enrolling during dehiscence; compressed, becoming woody. The mature valves without prominent venation. Seeds not arillate; with a straight or slightly oblique radicle.
Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. Leaf girders absent. Laminae isobilateral, with adaxial and abaxial palisades, or dorsiventral. Mesophyll without unaligned fibres or sclereids. Minor veins mainly with abundant accompanying fibres.
Leaf lamina epidermes. Epidermal crystals not seen either adaxially or abaxially. Simple unbranched hairs not seen. No compound or branched eglandular hairs seen. Capitate glands not seen. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section, or markedly sinuous in high-focus optical section; not conspicuously pitted; of medium thickness. Stomata adaxially very rare. Abaxial: Abaxial stomata predominantly paracytic. Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls straight, or gently undulating; not conspicuously pitted in optical section; staining normally with safranin; thin.
Pollen ultrastructure. Tectum striate; reticulate striate. Length of colpi greater than one half pole to pole distance.
Species number and distribution. 3 species (O. micranthum, O. normandii and O. romeroi). Equatorial West Africa.
Tribe. Detarieae (Amherstieae of Cowan and Polhill 1981); Amherstieae clade of Bruneau et al. (2008).
Miscellaneous. Illustrations: • O. micranthum: Aubréville, Flore du Gabon (1968).
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 classification. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1993 onwards. The genera of Leguminosae-Caesalpinioideae and Swartzieae: descriptions, illustrations, identification, and information retrieval. In English and French. Version: 22nd March 2017. delta-intkey.com/caes’.