Polystemma, Decaisne, 1844

Hernández-Barón, Gerald Matus, Juárez, Diana Isabel Trujillo & Steinmann, Victor W., 2023, Polystemma stevensii (Apocynaceae, Asclepiadoideae), a new species from Michoacán, Mexico, Phytotaxa 613 (2), pp. 194-200 : 199

Key to species of Polystemma of Michoacán, Mexico

1. Plants suffruticose, although vining at the branch ends; leaf blades less than 2 cm long and wide; flowers with the corolla lobes abaxially reticulate yellow-blackish or burgundy red ................................................................................................. P. fishbeiniana

- Plants vining; leaf blades more than 2 cm long and wide; flowers with the corolla lobes abaxially not reticulate...........................2

2. Corona lobes with a pair of falcate appendages ........................................................................................................ P. guatemalense

- Corona lobes with a pair of filiform appendages ...............................................................................................................................3

3. Corolla lobes ovate, glabrous adaxially, corolla tube purple, gynostegial corona fused at the base but without a discontinuous flat ring, style apex flat ....................................................................................................................................................... P. viridiflorum

- Corolla lobes lanceolate, sericeous adaxially, corolla tube white or yellowish, gynostegial corona fused at the base to form a discontinuous flat ring, style apex conspicuously globose................................................................................................ P. stevensii