| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Plagiosiphon Harms

Tripetalanthus A. Chev.

Type species: P. discifer Harms.

Habit and leaf form. Shrubs; unarmed.

Phyllotaxy spiral. The leaves compound; pinnate (two- to many-jugate), or bifoliolate (rarely); paripinnate; with adaxially grooved rachides. The leaflets somewhat leathery, often emarginate, many per leaf to few per leaf; opposite or sub-opposite; sessile to sub-sessile; markedly asymmetrical; without a continuous marginal nerve. Stipels absent.

Inflorescence and floral morphology. The inflorescences axillary; unbranched; elongated, several-flowered simple racemes. The flowers distichous. Bracts absent or minute. Bracteoles present; petaloid, suborbicular, small, not enclosing the flower buds to relatively large and enclosing the flower buds; persistent beyond anthesis; not valvate; free.

The flowers small; hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx; white or green. Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present; asymmetrically tubular (the tube basally ventricose on one side). The perianth comprising distinct calyx and corolla. Calyx 4; covering the rest of the flower in bud; polysepalous; more or less regular; members imbricate. Corolla present; slightly irregular, or very irregular; subspathulate, 5; without greatly reduced members; polypetalous. Petals sessile. Disk present and conspicuous. 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 free part pilose). Stigma small, subcapitellate on the filiform style, which is asally pilose. Ovules few (4–5).

Fruit, seed and seedling. Fruit a two-valved pod; compressed, obliquely oblong, mucronate,; valves twisting and enrolling during dehiscence. The mature valves with conspicuous, prominent, raised venation; conspicuous venation not predominantly longitudinal. Seeds not arillate; with a straight or slightly oblique radicle; amyloid-positive.

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 absent. Leaf girders absent. Laminae dorsiventral. Mesophyll exhibiting fibres or sclereids which are unaligned with the vascular bundles. 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 markedly sinuous in high-focus optical section; not conspicuously pitted; medium-thick. Stomata adaxially very rare. Abaxial: Abaxial stomata not predominantly paracytic (imperfect-paracytic). Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; staining normally with safranin; of medium thickness.

Pollen ultrastructure. Tectum striate; pole to pole striate. Length of colpi greater than one half pole to pole distance.

Species number and distribution. 5 species (P. discifer, P. emarginatus, P. gabonensis, P. longitubus, P. multijugus). Tropical Africa.

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

Miscellaneous. Illustrations: • Plagiosiphon longitubus and P. multijugus: Aubréville, Flore du Gabon (1968). • Plagiosiphon emarginatus, 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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