| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Hymenostegia (Benth.) Harms

Dipetalanthus A. Chev. Currently including Micklethwaitia (Harms) Lewis & Schrire

Type species: H. floribunda (Benth.) Harms.

Habit and leaf form. Trees, or shrubs (mostly with imbricate bud scales); unarmed.

Phyllotaxy spiral. The leaves compound; usually pinnate, or bifoliolate (? - rarely); paripinnate. The leaflets many per leaf to few per leaf ((4-)8(-50)); opposite or sub-opposite (usually), or alternate (rarely); sessile to sub-sessile; when subsessile, without noticeably twisted petiolules; symmetrical or nearly so; 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. Stipels absent.

Inflorescence and floral morphology. The inflorescences axillary, or terminal; unbranched, or branched; of racemose units; simple racemes, or panicles. The flowers not distichous. Bracteoles present (narrow to broad, at or near the top of the pedicel except in Micklethwaitia, petaloid); usually relatively large and enclosing the flower buds; persistent beyond anthesis (except in Micklethwaitia); not valvate; free.

The flowers small; hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx, or in the corolla, or in the androecium, or in the calyx, in the corolla, and in the androecium (in combinations). Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present. The perianth comprising distinct calyx and corolla. Calyx 4; covering the rest of the flower in bud; not Swartzieae type; polysepalous; more or less regular; members imbricate. Corolla present; very irregular; 1–5 (usually 2–3 being well developed, or 4–5 in Micklethwaitia); including greatly reduced members, or without greatly reduced members; polypetalous. Petals rarely green, usually white to yellow. Disk absent. The androecium comprising 10–25 members; members all free of one another; comprising only fertile stamens. Fertile stamens 10, or 16–25 (rarely). Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary stipitate; eccentric, with the stipe adnate. Stigma not dilated (the style filiform). Ovules few (2–3).

Fruit, seed and seedling. Fruit a two-valved pod; not internally septate; valves twisting and enrolling during dehiscence; winged longitudinally, or not noticeably winged; compressed, leathery, becoming woody, or not becoming woody. The mature valves without prominent venation. Seeds non-endospermic; not arillate; with a straight or slightly oblique radicle; amyloid-positive. Cotyledons not flat; of Type 4; with a vascular system in one plane; epigeal.

Transverse section of lamina. Druses common in the mesophyll, absent from 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 present, or not seen either adaxially or abaxially; druses. Simple unbranched hairs common, or not seen. 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; (at least some of them) thin-walled; hair feet all simple, without vertical walls. Basally bent hairs present. Adaxial: Adaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; conspicuously pitted, or not conspicuously pitted; thick. Stomata adaxially very rare. Abaxial: Abaxial stomata predominantly paracytic. Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; conspicuously pitted in optical section; staining normally with safranin; thin.

Wood anatomy. Wood not storied. Intervascular pits very small, or medium to large.

Pollen ultrastructure. Tectum striate; pole to pole striate.

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

Species number and distribution. About 16 species. Tropical Africa.

Tribe. Detarieae.

Miscellaneous. Illustrations: • Hymenostegia laxiflora: Leonard, in Fl. du Congo Belge (1952). • H. klainei and H. ngounyensis: Aubréville, Flore du Gabon (1968). • H. mundungu, H. neoaubrevillei and H. pellegrinii: Aubréville, Flore du Gabon (1968). • Hymenostegia afzelii, H. brachyura and H. breteleri: Aubréville, Flore du Cameroun (1970). • Hymenostegia laxiflora, flower (Cowan & Polhill, 1981). • Hymenostegia afzelii, 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’.

Contents