Senna Mill.

Trees, shrubs, or herbs. Leaves 1-paripinnate, petioled; leafstalk glandular or eglandular, the glands sessile and spheroid or ovoid, or clavate-stipitate to cylindric; leaflets few to numerous; stipules usually small and caducous, occasionally persistent. Inflorescence(s) either axillary racemes that are aggregated in compound, corymbose, or thyrsiform forms or are sometimes reduced to 1-2 flowers, solitary or paired in leaf axils; bracts usually

caducous.  Sepals spirally sequential, upward accrescent, usually yellowish green; corolla of slightly or conspicuously unequal petals, zygomorphic or irregular, yellow to orange-yellow; androecium of either 10 fertile stamens or 10 heteromorphic stamens, the upper 3-5 staminodal and ordinary, the remainder functional, of these the lower 3 longer and subequal to the petals; filaments shorter than anthers to twice as long, straight or curved but none sigmoid. Legume either indehiscent, sometimes breaking irregularly, or inertly dehiscent, usually oblong, laterally compressed to cylindric, sometimes conspicuously winged, usually septate between seeds, ligneous to papery, glabrous, occasionally pubescent. Seeds usually numerous. Pantropic, about 250 species. (ISE)

Notes: The generic names Cassia and Senna have been applied to the same plants by taxonomists over the years. The names used here follow the taxonomic key in WU1. In this key, the plants in the genus Cassia have “filaments of 3 lower stamens sigmoid-curved and elongate”; plants in the genus Senna have “filaments of all stamens straight”.

1. Leaves eglandular

     2. Leaflets 1/2 " or shorter.............................................................................................S. polyphylla

     2. Leaflets longer than 1/2"

          3. Herb or subshrub; fruit conspicuously 4-winged..................................................S. alata

          3. Shrub or tree; fruit not 4-winged

4. Tree; fruit bent at base, stiffly coriaceous, 8" or longer.................................. S. siamea

4. Shrub; fruit 4-1/2" or shorter..................................................................... ..... S. didymobotrya

1. Leaves with 1 or more petiolar glands

     5. Leaf glands at the base of the petiole........................................................................ S. ligustrina

     5. Leaf glands on the rachis between the leaflet pairs

   6. Leaf glands between the lower two pairs or all pairs of leaflets.......................... S. surattensis

   6. Leaf glands usually solitary between the lowermost pair of leaflets

7. Pinnate leaves with 2 pairs of leaflets............................................................... S. fruticosa

7. Pinnate leaves with 3 or more pairs of leaflets

8. Leaflets 1/2"-1"...........................................................................................S. mexicana

8. Leaflets longer than 1-1/4"..........................................................................S. bicapsularis