| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Senna Mill.

~ Cassia subgen Senna (Mill.) Benth.

Adipera Raf., Cathartocarpus Pers., Cowellocassia Britt., Desmodiocassia B. & R., Ditremexia Raf., Adipera Raf., Chamaefistula G. Don, Chamaesenna Raf., Cowellocassia Britt., Desmodiocassia B. & R., Ditremexia Raf., Earleocassia Britt., Echinocassia B. & R., Emelista Raf., Gaumerocassia Britt., Herpetica Raf., Isandrina Raf., Leonocassia B. & R., Palmerocassia Britt., Panisia Raf., Peiranisia Raf., Phragmocassia B. & R., Pseudocassia B. & R., Psilorhegma (Benth.) B. & R., Pterocassia B. & R., Sciacassia Britt., Sericeocassia Britt., Tharpia B. & R., Vogelocassia Britt., Xerocassia B. & R.

Habit and leaf form. Trees, or shrubs, or herbs (often herbaceous with woody base, sometimes monocarpic); unarmed; exhibiting some leaves reduced to phyllodes, and/or with leaflets tiny and early-caducous (sometimes, in Australia), or without leaves reduced to phyllodes, the leaflets normally well developed and persistent.

Phyllotaxy spiral. The leaves compound (usually); often with petiolar nectariferous glands, pinnate (usually), or bifoliolate (in Australia); paripinnate. The leaflets many per leaf to few per leaf; opposite or sub-opposite; petiolulate; without noticeably twisted petiolules; markedly asymmetrical to symmetrical or nearly so; pinnately veined, with a predominant ‘midrib’. Stipules present, persistent and conspicuous in mature leaves, or absent or early caducous or very inconspicuous in mature leaves (?); if present, leafy, or membranous; not connate. Stipels absent.

Inflorescence and floral morphology. The flowers aggregated into inflorescences, or solitary. The inflorescences axillary, or terminal; unbranched, or branched; ambiguously of racemose units, or of cymose units; simple racemes, or panicles (often becoming corymbose-paniculate towards the ends of the branchlets, rarely cauliflorous). The flowers not distichous. Bracts absent at anthesis, or persistent beyond anthesis (?). Bracteoles absent; absent at anthesis.

The flowers hermaphrodite; pentamerous, or not pentamerous throughout; departing from pentamery commonly in the androecium; coloured. Floral tube length relative to total hypanthium + calyx length when applicable, about 0.25. Hypanthium absent, the androecium hypogynous. The perianth comprising distinct calyx and corolla. Calyx 5; covering the rest of the flower in bud; gamosepalous, or polysepalous (?); more or less regular, or markedly irregular; members imbricate. Corolla present; slightly irregular to very irregular; spreading, 5; without greatly reduced members; polypetalous. Petals all clawed, or clawed to sessile; imbricate; imbricate-ascending; white (rarely), or yellow (usually). Disk absent. The androecium comprising 5–10 members; without the three long-filamented, short-anthered abaxial stamens characteristic of Cassia (the some species approach the Cassia syndrome: e.g., S. occidentalis, with three very long, apically dehiscent stamens); declinate; members all free of one another; members all more or less equal in length (rarely), or markedly unequal (frequently); including staminodia to comprising only fertile stamens (the androecium commonly accrescent towards the adaxial side of the flower with the adaxial members commonly dwindling to staminodes, but without the three sigmoidally-curved, short-anthered members characteristic of Cassia sensu stricto). Fertile stamens 5–10 (the straight filaments shorter than or at least not over twice as long as the anthers). Anthers attached at the base of the connective; dehiscing apically via pores or short slits (the thecae glabrous along the sutures). Ovary sessile or subsessile, or stipitate; free. Stigma not dilated. Ovules numerous.

Fruit, seed and seedling. Fruit a follicle, or a two-valved pod, or indehiscent; straight, or curved; internally septate, or not internally septate (the cavity transversely septate or not, the seeds uni- or rarely biseriate); without markedly twisting or enrolling valves; winged longitudinally (sometimes, along the sutures or the valves), or not noticeably winged; becoming woody, or not becoming woody (terete, 4-angled, turgid or plano-convex, the valves varying from papery to leathery or ligneous). The mature valves with conspicuous, prominent, raised venation, or without prominent venation; conspicuous venation predominantly longitudinal, or not predominantly longitudinal. Seeds compressed laterally, endospermic; not arillate (funicle filiform); with a straight or slightly oblique radicle; amyloid-negative; with galactomannan. Cotyledons of Type 1, or Type 2, or Type 3 (?); with a vascular system in one plane; epigeal.

Transverse section of lamina. Leaves without conspicuous phloem transfer cells in the minor veins. Druses common in the mesophyll, absent from the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. 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; scabrid, or smooth. No compound or branched eglandular hairs seen. Capitate glands not seen. Hooked hairs present, or not seen. Cassieae-type leaf pseudo-glands not seen. Expanded and embedded hair-feet absent. Basally bent hairs present. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section; conspicuously pitted; of medium thickness. Stomata adaxially very rare. Abaxial: Abaxial stomata predominantly paracytic. Abaxial epidermis papillate interveinally, or not papillate; with the papillae not over-arching the stomata. Abaxial interveinal epidermal cell walls straight, or gently undulating; not conspicuously pitted in optical section; scarcely staining with safranin; thin.

Wood anatomy. Wood with septate fibres, or without septate fibres; not storied; without normal intercellular canals; without traumatic canals. Intervascular pits medium to large.

Pollen ultrastructure. Tectum punctate, or reticulate; smooth punctate, or puncticulate, or rugulose punctate; rugulose reticulate. Length of colpi greater than one half pole to pole distance, or less than one half pole to pole distance (rarely).

Cytology. Basic chromosome number, x = 14. 2n = 22, or 24, or 26, or 28.

Species number and distribution. About 240 species. Circumtropical: most numerous in the Americas but well represented in Africa and Australia, less conspicuous in Asia and Oceania, a few represented even in desert and cold temperate N. and S. America.

Tribe. Cassieae.

Comments. Widely cultivated.

Miscellaneous. Illustrations: • Senna occidentalis: Bot. Reg. 83, 1815. • Senna floribunda var. herbertiana (as Cassia herbertiana): Bot. Reg. 1422, 1831. • cf. Senna pallida as Cassia biflora): Bot. Reg. 1310, 1830. • Senna floribunda or S. septemtrionalis as Cassia floribunda (floral details): Baillon, Histoire des Plantes 2 (1870). • Senna bacillaris (as Cathartocarpus bacillus): Bot. Reg. 881, 1825. • S. bacillaris (as Cassia fruticosa): Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna didymobotrya: Steyaert, in Fl. du Congo Belge (1952). • cf. S. odorata (as Cassia australis), Bot. Reg. 1322, 1830. • Senna angulata (as Cassia): Fl. Brasiliensis 15 (1870). • Senna uniflora with Chamaecrista calcioides (as Cassia spp.): Fl. Brasiliensis 15 (1870). • Senna petersiana as Cassia: Engler & Drude, Pflanzenwelt Afrikas 9 (1915). • Senna singueana (as C. goratensis): Engler & Drude, Pflanzenwelt Afrikas 9 (1915). • Senna bacillaris, S. uniflora (as C. sericea), S. pentagonia and S. marylandica (with Labichea lanceolata): Nat. Pflanzenfam. III (1894). • cf. Senna italica (as Cassia obovata): Baillon, Histoire des Plantes 2 (1870). • Senna hirsuta and S. pentagonia (as Cassia spp.): Fl. Brasiliensis 15 (1870). • Senna nicaraguensis (as Cassia): Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna hirsuta var. hirta (as Cassia): Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna occidentalis (as Cassia): Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna williamsii (as Cassia):: Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna multijuga (as Cassia): Schery, Ann. Miss. Bot. Gard. 38 (1951). • Senna alexandrina (as Cassia acutifolia and C. angustifolia) and C. chamaecrista (= ?): Nat. Pflanzenfam. III (1894). • Senna (Cassia) leptocarpa, 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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