Leaves alternate, paripinnate or reduced to phyllodes; leaflets 1–16 pairs, terete to linear or obovate, rachis usually with glands present; petiole terete or laterally compressed.
Inflorescences axillary, racemose. Sepals 5, subequal, green or yellowish. Petals 5, subequal or not, clawed, yellow or golden. Stamens 10; anthers basifixed, bilaterally symmetric, all equal or 2 or 3 lower longer than the rest; filaments subequal or 2 or 3 lower ones slightly longer, or much longer and C-curved.
Pods variable, either flat or cylindrical and dehiscent [or woody and indehiscent].
| | Key to the species | |
| 1 | Leaflets 3–15 pairs | 2 |
| 1 | Leaflets 16–37 pairs | Senna multijuga |
| 2 | Leaves terete and silvery in colour | Senna artemisioides group |
| Leaves not terete and not silvery
Back to 1 | 3 |
| 3 | Gland(s) located at or near the base of the petiole | 4 |
| Glands located between leaflet pairs or absent
Back to 2 | 6 |
| 4 | Peduncles <6 mm long, pods >9 cm long | Senna occidentalis |
| Peduncles >9 mm long, pods <9 cm long
Back to 3 | 5 |
| 5 | Gland on petiole erect, higher than broad | Senna clavigera |
| Gland on petiole broader than high
Back to 4 | Senna barclayana |
| 6 | Glands absent from leaves or inconspicuous beneath thick indumentum | 7 |
| Leaves with glands between leaflet pairs
Back to 3 | 9 |
| 7 | Floral bracts dark brown or black, persistent | Senna didymobotrya |
| Floral bracts pale or green, caducous
Back to 6 | 8 |
| 8 | Plant pubescent except for inner flower parts; leaf glands present but small and inconspicuous below dense indumentum | Senna notabilis |
| Plant glabrous; glands on leaves absent
Back to 7 | Senna pleurocarpa |
| 9 | Flowers with only 6 or 7 anthers fertile (3 upper always reduced or absent), of 2 or 3 different sizes, sometimes beaked; pods cylindrical | 10 |
| Flowers with all 10 anthers fertile, sub-equal, truncate; pods flat
Back to 6 | 12 |
| 10 | Gland 1 between basal pair of leaflets | Senna pendula |
| Glands 2–4, between the lower pairs of leaflets
Back to 9 | 11 |
| 11 | Leaves pubescent, leaflets 6–8 pairs, leaflets acute and mucronate | Senna multiglandulosa |
| Leaves glabrous, leaflets 4–5 pairs, leaflets with an acuminate apex
Back to 10 | Senna septemtrionalis |
| 12 | Petals greater than or equal to 11 mm long; seeds glossy or dull | 13 |
| Petals <11 mm long; seeds dull or rarely lustrous
Back to 9 | Senna phyllodinea |
| 13 | Petals pubescent on the outer surface; stipules broadly falcate, persistent; whole plant ± pruinose; pod without ridges on the inner faces of the valves | Senna glutinosa |
| Petals glabrous on the outer surface, stipules acicular, caducous, plant never pruinose; pod with ridges on the inner faces of the valves
Back to 12 | 14 |
| 14 | Petioles 20–40 mm long, leaflet pairs c. 15 mm apart on the rachis. | Senna acclinis |
| Petioles 2–15 mm long, leaflet pairs <11 mm apart on the rachis
Back to 13 | 15 |
| 15 | Peduncles 1–3 cm long; glands only between the lowermost 1 or 2 pairs of leaflets | Senna coronilloides |
| Peduncles 2–9 cm long; glands between all pairs of leaflets
Back to 14 | 16 |
| 16 | Petioles mostly less than 5 mm long; leaflets linear to narrow-elliptic, usually revolute at the margins, 1–4 mm wide, usually pubescent | Senna aciphylla |
| Petioles more than 5 mm long; leaflets lanceolate to elliptic, rarely slightly recurved at the margins, 5–10 mm wide; not obviously pubescent, sometimes sparsely hairy
Back to 15 | Senna barronfieldii |
