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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Pachyelasma Harms

Type species: P. tessmannii (Harms) Harms).

Habit and leaf form. Trees; unarmed.

The leaves compound; bipinnate; mostly with opposite or sub-opposite pinnae (with 2–4 pairs); with alternate leaflets. The leaflets petiolulate; somewhat leathery, oblong to oblanceolate-oblong; pinnately veined, with a predominant ‘midrib’. Stipules absent or early caducous or very inconspicuous in mature leaves; membranous. Stipels absent.

Inflorescence and floral morphology. The inflorescences unbranched; elongated, spiciform simple racemes. Bracts absent at anthesis. Bracteoles absent; absent at anthesis.

The flowers malodorous, small; hermaphrodite; pentamerous; coloured. Hypanthium present; broadly cupular. The perianth comprising distinct calyx and corolla. Calyx shortly ciliolate, 5; not covering the rest of the flower in bud; polysepalous; members broad, imbricate. Corolla present; regular to slightly irregular; 5; without greatly reduced members; polypetalous (the petals about twice as long as the calyx segments). Petals sessile; all similar, obovate-oblong to obovate, imbricate; imbricate-ascending; red. The androecium comprising 10 members; not declinate; members all free of one another (the free filaments glabrous); members all more or less equal in length; comprising only fertile stamens. Fertile stamens 10. Anthers attached at the base of the connective (their bases scarcely sagittate); dehiscing introrsely. Ovary sessile or subsessile (the style shortish, curved-subulate); free. Stigma not dilated. Ovules 2-seriate, numerous.

Fruit, seed and seedling. Fruit indehiscent; 10–15 seeded, large, compressed, lanceolate to oblong-lanceolate, straight to curved; internally septate; without markedly twisting or enrolling valves; becoming woody. The mature valves with conspicuous, prominent, raised venation; conspicuous venation predominantly longitudinal (with 4 strong ribs reinforcing the angles, one adjoining each suture). Seeds endospermic; not arillate; with a straight or slightly oblique radicle; amyloid-negative. Cotyledons epigeal.

Transverse section of lamina. Leaves without conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis present. 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 not seen. No compound or branched eglandular hairs seen. Capitate glands not seen. Expanded and embedded hair-feet absent. Adaxial: Adaxial interveinal epidermal cell walls 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; conspicuously pitted in optical section, or not conspicuously pitted in optical section; staining normally with safranin; thick.

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

Species number and distribution. 1 species (P. tessmannii). West Africa.

Tribe. Caesalpinieae.

Miscellaneous. Illustrations: • P. tessmannii: Bot. Jahrb. 49 (1913).

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.’.