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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Acrocarpus Wight & Arn.

Type species: A. fraxinifolius Wight & Arn.

Habit and leaf form. Trees; unarmed.

The leaves compound; bipinnate; with opposite or sub-opposite pinnae; with opposite or sub-opposite leaflets. The leaflets many per leaf; petiolulate; symmetrical or nearly so; pinnately veined, with a predominant ‘midrib’. Stipules absent or early caducous or very inconspicuous in mature leaves; if present, membranous; not connate. Stipels absent.

Inflorescence and floral morphology. The inflorescences axillary and terminal; unbranched and branched; of racemose units; simple racemes and panicles (simple axillary racemes and terminal panicles of 2–3). The flowers when branched, not distichous. Bracts small and caducous, absent at anthesis. Bracteoles present; small, not enclosing the flower buds; absent at anthesis.

The flowers large; hermaphrodite; actinomorphic; pentamerous; coloured (greenish yellow). Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present; conspicuous, saucer-shaped to cupular (the exposed part red). Calyx 5; covering the rest of the flower in bud, or not covering the rest of the flower in bud; polysepalous; more or less regular; members slightly imbricate. Corolla present; regular to slightly irregular; 5; without greatly reduced members. Well developed petals 5. Corolla polypetalous. Petals narrow, much exceeding the calyx. Disk present and conspicuous. The androecium comprising 5 members; members all free of one another; comprising only fertile stamens. Fertile stamens alternisepalous, 5. Anthers attached well above the base of the connective; dehiscing introrsely. Ovary stipitate; free. Stigma not dilated (the style short). Ovules numerous.

Fruit, seed and seedling. Fruit a two-valved pod; straight; without markedly twisting or enrolling valves; winged longitudinally (on the adaxial suture); 1 winged; not becoming woody. Seeds endospermic; small, arillate (sometimes winged); with a straight or slightly oblique radicle; amyloid-negative. Cotyledons of Type 2; epigeal.

Transverse section of lamina. Leaves without conspicuous phloem transfer cells in the minor veins. Druses common in the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. Leaf girders absent. Laminae 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 common; smooth. No compound or branched eglandular hairs seen. Capitate glands not seen. Hooked hairs not seen. Cassieae-type leaf pseudo-glands not seen. Expanded and embedded hair-feet absent. Basally bent hairs absent. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section; conspicuously pitted; thick. 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; scarcely staining with safranin; medium-thin.

Pollen ultrastructure. Tectum punctate; rugulose punctate. Length of colpi greater than one half pole to pole distance (no margocolpus).

Cytology. Basic chromosome number, x = 12. 2n = 24.

Species number and distribution. 1 species (A. fraxinifolius). Indomalayan region.

Tribe. Caesalpinieae.

Comments. Widely cultivated.

Miscellaneous. Illustrations: • Acrocarpus fraxinifolius: Wight, Ic. Pl. Ind. Orient. (1840).

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.’.