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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Amherstia Wall.

Type species: A. nobilis Wall.

Habit and leaf form. Trees; unarmed.

Phyllotaxy distichous. The leaves compound; pinnate; paripinnate. The leaflets opposite or sub-opposite; petiolulate; without noticeably twisted petiolules; symmetrical or nearly so; pinntely veined, with a predominant ‘midrib’. Stipules absent or early caducous or very inconspicuous in mature leaves (deciduous); leafy, or membranous; connate. Stipels absent.

Inflorescence and floral morphology. The inflorescences terminal; unbranched; simple racemes (many-flowered, long, lax and pendulous). The flowers on long pedicels, not distichous. Bracts absent at anthesis. Bracteoles present; coloured, relatively large and enclosing the flower buds; persistent beyond anthesis; valvate.

The flowers very showy; hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx, or in the calyx and in the corolla; coloured. Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present; long tubular. Calyx petaloid, 4; covering the rest of the flower in bud; polysepalous; more or less regular; members imbricate. Corolla present; very irregular (the uppermost petal broad and obcordate, up to 7 cm long, the laterals oblong cuneate, the lower minute); 3 (rarely), or 5; including greatly reduced members; polypetalous. Petals imbricate; imbricate-ascending; red. The androecium comprising 10 members; with united members (9 united, 1 free); members markedly unequal; comprising only fertile stamens. Fertile stamens 10. Anthers attached well above the base of the connective. Ovary stipitate; eccentric, with the stipe adnate (the style filiform). Stigma not dilated. Ovules numerous.

Fruit, seed and seedling. Fruit a two-valved pod; curved; without markedly twisting or enrolling valves; becoming woody. Seeds non-endospermic; not arillate; amyloid-positive.

Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins.

Pollen ultrastructure. Tectum striate; interwoven striate. Length of colpi greater than one half pole to pole distance.

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

Species number and distribution. 1 species (A. nobilis). Burma.

Tribe. Detarieae (Amherstieae of Cowan and Polhill 1981); Amherstieae clade of Bruneau et al. (2008).

Comments. Widely cultivated.

Miscellaneous. Illustrations: • A. nobilis: Bot. Mag 75 (1849). • A. nobilis: Baillon, Histoire des Plantes 2 (1870). • A. nobilis, e.m. scanned pollen (Graham & Barker, 1981).

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.’.