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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Hylodendron Taub.

Type species: H. gabunense Taub.

Habit and leaf form. Large trees (with large bud scales leaving conspicuous scars at the shoot bases); unarmed.

Phyllotaxy spiral. The leaves compound; pinnate; imparipinnate. The leaflets many per leaf (9–15); oblong, marginally pellucid-punctate, alternate; petiolulate; without noticeably twisted petiolules; with a strong, continuous marginal nerve. Stipules ultimately deciduous, large, very long linear, spirally folded around the bud; membranous. Stipels absent.

Inflorescence and floral morphology. The inflorescences axillary and terminal; unbranched; short simple racemes. The flowers distichous. Bracts broadly ovate, leathery, striate, closely imbricate and covering the flower buds. Bracteoles present (linear, at the base of the calyx); small, not enclosing the flower buds; absent at anthesis; not valvate; free.

The flowers small; hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx and in the corolla, or in the calyx, in the corolla, and in the androecium. Hypanthium absent, the androecium hypogynous. The perianth exclusively sepaline. Calyx 4; covering the rest of the flower in bud; polysepalous; more or less regular; members concave, slightly imbricate, or not imbricate (subvalvate). Corolla absent. Disk absent. The androecium comprising 8(–10) members; members all free of one another; members markedly unequal (alternately longer and shorter); comprising only fertile stamens. Fertile stamens 8(–10). Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary sessile or subsessile; free. Stigma small but dilated (capitellate on the linear-subulate stigma). Ovules solitary to few.

Fruit, seed and seedling. Fruit samaroid, indehiscent (with 1–2 distal seeds); slightly curved; winged proximally to the single seed (or sometimes to two seeds, via the flattened base); narrowly oblong, thin, glabrous, flat, not becoming woody. The mature valves with conspicuous, prominent, raised venation; conspicuous venation transverse and reticulate, not predominantly longitudinal. Seeds 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. Leaves with conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities (gland-dots) common (towards the margins); without a lining of epithelium. 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; prisms. 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 markedly sinuous in high-focus optical section; not conspicuously pitted; of medium thickness. 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; not conspicuously pitted in optical section; scarcely staining with safranin; thin.

Wood anatomy. Wood without normal intercellular canals; without traumatic canals.

Pollen ultrastructure. Tectum punctate; rugulose punctate.

Species number and distribution. 1 species (H. gabunense). Tropical Africa.

Tribe. Detarieae; Detarieae sensu stricto clade of Bruneau et al. (2008).

Miscellaneous. Illustrations: • H. gabunense, with Pterygopodium (= Oxystigma) oxyphyllum: Aubréville, Flore du Gabon (1968). • H. gabunense, e.m. scanned pollen (Graham & Barker, 1981).


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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. delta-intkey.com/caes’.

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