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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Gabonius Wieringa & Mackinder

Hymenostegia p.p. (H. ngouniensis Pellegr.)

Type species: G. ngouniensis Wieringa & Mackinder.

Habit and leaf form. Trees, or shrubs (without imbricate bud scales); unarmed.

Phyllotaxy spiral. The leaves compound; pinnate (mostly), or bifoliolate (rarely); with opposite or sub-opposite pinnae; paripinnate. The leaflets many per leaf to few per leaf ((4-)10–12(-14)); opposite or sub-opposite; sessile to sub-sessile (more or less 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 (present but caducous); membranous; touching basally, not connate. Stipels absent.

Inflorescence and floral morphology. The inflorescences axillary and terminal; simple racemes. The flowers not distichous. Bracts absent at anthesis (caducous). Bracteoles present (borne at or near the top of the pedicel); broad, petaloid, relatively large and enclosing the flower buds; persistent beyond anthesis; valvate (at least, touching along the margins prior to anthesis); free.

The flowers small; hermaphrodite; pentamerous. Hypanthium present (6–9 mm deep). The perianth comprising distinct calyx and corolla. Calyx 4, or 5 (?); covering the rest of the flower in bud; polysepalous; more or less regular; members imbricate. Corolla present; very irregular (the three adaxial and lateral members 10–13 mm long and similar in size, the two abaxials only about 4 mm long); 5; without greatly reduced members; polypetalous. Petals clawed; imbricate; white (the smaller abaxials), or white and yellow (the adaxials and laterals). Disk absent. The androecium comprising 10 members; members all free of one another; comprising only fertile stamens. Fertile stamens 10. Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary stipitate; eccentric, with the stipe adnate (the stipe fused for most of its length to the adaxial side of the hypanthium). Stigma dilated. Ovules few.

Fruit, seed and seedling. Fruit a two-valved pod (compressed, trapezoid, rather large compared with those of related genera); not internally septate; valves twisting and enrolling during dehiscence. 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.

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. 1 species (G. ngouniensis). Gabon.

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


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. delta-intkey.com/caes’.

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