| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Brachystegia Benth.

Type species: B. spiciformis Benth.

Habit and leaf form. Trees (with the young leaves often brightly coloured); unarmed.

Phyllotaxy distichous, or spiral. The leaves compound; pinnate; paripinnate. The leaflets many per leaf, or few per leaf; opposite or sub-opposite; sessile to sub-sessile; with markedly twisted petiolules, or without noticeably twisted petiolules (rarely); markedly asymmetrical; pinntely veined, with a predominant ‘midrib’; without a continuous marginal nerve. Stipules absent or early caducous or very inconspicuous in mature leaves, or present, persistent and conspicuous in mature leaves; leafy, or membranous; connate, or not connate. Stipels present, or absent.

Inflorescence and floral morphology. The inflorescences usually terminal (rarely lateral on older branchlets); unbranched, or branched; when branched, probably of racemose units; simple racemes, or panicles. The flowers distichous (rarely), or not distichous. Bracts absent at anthesis. Bracteoles present; relatively large and enclosing the flower buds; persistent beyond anthesis; valvate.

The flowers hermaphrodite; not pentamerous throughout (the calyx and corolla together comprisng 1–11 tepals, often rudmentary or absent); departing from pentamery in the calyx and in the corolla. Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present; short; cupular. The perianth comprising distinct calyx and corolla, or exclusively sepaline, or of ‘tepals’, or entirely vestigial. Calyx obscurely present to absent; not covering the rest of the flower in bud; if recognisable, polysepalous. Corolla present, or absent (or not identifiable as such); if recognisable, very irregular; when distinguishable, 1–3(–5); including greatly reduced members; polypetalous. Petals sessile. Disk present and conspicuous, or absent. The androecium comprising (9–)10(–18) members; with united members, or members all free of one another (often obscurely diadelphous); members all more or less equal in length, or markedly unequal; including staminodia, or comprising only fertile stamens. Fertile stamens (9–)10(–18). Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary stipitate; free. Stigma dilated (but tiny). Ovules numerous.

Fruit, seed and seedling. Fruit a two-valved pod; valves twisting and enrolling during dehiscence; narrowly winged longitudinally; becoming woody. The mature valves with conspicuous, prominent, raised venation, or without prominent venation; conspicuous venation if present, oblique or reticulate, not predominantly longitudinal. Seeds non-endospermic; with a straight or slightly oblique radicle; amyloid-positive. Cotyledons of Type 4; with a vascular system in one plane; epigeal.

Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities (gland-dots) common, or absent. Adaxial hypodermis absent. Leaf girders common (the veins transcurrent), or 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; scabrid. 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 present, or absent; all medium to thick-walled, or (at least some of them) thin-walled; hair feet (at least some of them) complex with vertical walls, or all simple, without vertical walls. Basally bent hairs absent. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section; conspicuously pitted, or not conspicuously pitted; medium-thin. Stomata adaxially common and widespread, or adaxially very rare. Abaxial: Abaxial stomata predominantly paracytic. Abaxial epidermis papillate interveinally, or not papillate; with the papillae not over-arching the stomata. Abaxial interveinal epidermal cell walls straight, or gently undulating, or markedly sinuous in high-focus optical section; conspicuously pitted in optical section, or not conspicuously pitted in optical section; staining normally with safranin; of medium thickness to medium-thin.

Wood anatomy. Wood without septate fibres; storied; without normal intercellular canals; without traumatic canals. Intervascular pits medium to large.

Pollen ultrastructure. Tectum reticulate; strongly irregularly coarse-reticulate. Length of colpi greater than one half pole to pole distance. Foot layer of pollen wall smooth.

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

Species number and distribution. About 35 species. Tropical and southern Africa.

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

Miscellaneous. Illustrations: • Brachystegia spiciformis: Brenan, Fl. Tropical East Africa (1967). • B. spiciformis, assorted forms: Brenan, Fl. Tropical East Africa (1967). • Brachystegia microphylla: Brenan, Fl. Tropical East Africa (1967). • Brachystegia allenii: Brenan, Fl. Tropical East Africa (1967). • Brachystegia boehmii: Hoyle, in Fl. du Congo Belge (1952). • Brachystegia eurycoma and B. mildbraedii: Aubréville, Flore du Gabon (1968). • Brachystegia appendiculata: Engler & Drude, Pflanzenwelt Afrikas 9 (1915). • Brachystegia longifolia: Hook. Ic. Pl. 14 (1880–82). • Brachystegia longifolia, 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: 4th August 2019. delta-intkey.com’.

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