| Senna papillosa var. papillosa (Britton & Rose) H.S. Irwin & Barneby, 1982 |
| Senna pendula (Humb. & Bonpl. ex Willd.) H.S. Irwin & Barneby, 1982 |
| Senna pendula var. advena (Vogel) H.S. Irwin & Barneby, 1982 |
| Senna pendula var. glabrata (Vogel) H.S. Irwin & Barneby, 1982 |
| Senna pendula var. ovalifolia H.S. Irwin & Barneby, 1982 |
| Senna pendula var. pendula (Humb. & Bonpl. ex Willd.) H.S. Irwin & Barneby, 1982 |
| Senna pentagonia (Mill.) H.S. Irwin & Barneby, 1982 |
| Senna pentagonia var. pentagonia (Mill.) H.S. Irwin & Barneby, 1982 |
| Senna peralteana (Kunth) H.S. Irwin & Barneby, 1982 |
| Senna pilifera (Vogel) H.S. Irwin & Barneby, 1982 |
| Senna pilifera var. subglabra (S. Moore) H.S. Irwin & Barneby, 1982 |
| Senna pilosior (B.L. Rob. ex J.F. Macbr.) H.S. Irwin & Barneby, 1979 |
| Senna polyantha (Collad.) H.S. Irwin & Barneby, 1982 |
| Senna polyphylla (Jacq.) H.S. Irwin & Barneby, 1982 |
| Senna pumilio (A. Gray) H.S. Irwin & Barneby, 1979 |
| Senna purpusii (Brandegee) H.S. Irwin & Barneby, 1982 |
| Senna quinquangulata (Rich.) H.S. Irwin & Barneby, 1982 |
| Senna quinquangulata var. quinquangulata (Rich.) H.S. Irwin & Barneby, 1982 |
| Senna racemosa (Mill.) H.S. Irwin & Barneby, 1982 |
| Senna racemosa var. coalcomanica H.S. Irwin & Barneby, 1982 |