| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Piliostigma Hochst.

~ Bauhinia sensu lato, Bauhinia subgenus Elayuna, Locellaria Welw.

Elayuna Rafin.

Habit and leaf form. Trees, or shrubs (without tendrils); armed (with thorns, in the New World), or unarmed (in the palaeotropics).

Phyllotaxy distichous. The leaves two-lobed. Stipules absent or early caducous or very inconspicuous in mature leaves (early caducous); membranous (with small intrastipular trichomes); not connate.

Inflorescence and floral morphology. The inflorescences sometimes leaf-opposed; of P. thonningii branched; of racemose units; panicles. The flowers not distichous. Bracts small, persistent beyond anthesis. Bracteoles present; small, not enclosing the flower buds (very reduced); absent at anthesis to persistent beyond anthesis; not valvate; free.

The flowers hermaphrodite, or unisexual (then dioecious or polygamo-dioecious); pentamerous, or not pentamerous throughout; departing from pentamery in the calyx; coloured. Floral tube length relative to total hypanthium + calyx length about 0.75. Hypanthium present; short, turbinate. Calyx 2–5 (distally splitting irregularly into 2–5 lobes or teeth); covering the rest of the flower in bud; not Swartzieae type; gamosepalous; more or less regular, or markedly irregular; members not imbricate. Corolla present; slightly irregular; 5; without greatly reduced members (the petals subequal); polypetalous. Petals clawed, or sessile; imbricate; imbricate-ascending; white, or yellow. Disk absent. The androecium comprising 10 members; not declinate; members all free of one another; members markedly unequal (the members of the outer whorl longer in male flowers); including staminodia (in female-fertile flowers), or comprising only fertile stamens. The staminodia in female-fertile flowers, 10; very small. Fertile stamens in male and hermaphrodite flowers, 10. Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary stipitate; free. Stigma large and dilated. Ovules numerous.

Fruit, seed and seedling. Fruit a two-valved pod, or indehiscent; not drupaceous; linear-oblong, straight, or curved; without markedly twisting or enrolling valves; becoming woody. The mature valves with conspicuous, prominent, raised venation to without prominent venation; conspicuous venation if present, not predominantly longitudinal. Seeds endospermic; arillate (with two funicular lobes, one long and one short, the hilum crescentic); with a straight or slightly oblique radicle.

Transverse section of lamina. Leaves without conspicuous phloem transfer cells in the minor veins. Druses common in the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis present. Leaf girders common (the veins transcurrent). 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; smooth. 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; all medium to thick-walled; hair feet all simple, without vertical walls. Basally bent hairs absent. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section; not conspicuously pitted; medium-thin. Stomata adaxially very rare. Abaxial: Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls straight, or gently undulating; not conspicuously pitted in optical section; staining normally with safranin; thin.

Pollen ultrastructure. Tectum reticulate; verrucose reticulate. Length of colpi less than one half pole to pole distance.

Cytology. Basic chromosome number, x = 14. 2n = 24, or 26, or 28, or 42.

Species number and distribution. 6 species (e.g. P. malabaricum - all often referred to Bauhinia). Tropical Africa, Indomalayan region, Australia, tropical America.

Tribe. Cercideae.

Miscellaneous. Illustrations: • Piliostigma thonningii: Brenan, Fl. Tropical East Africa (1967). • P. thonningii, flower (Wunderlin & Larsen, 1981). • Piliostigma thonningii, 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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