The two species can be easily separated using the following identification key:

1. Leaves narrowly ovate to broadly ovate, pinnatisected to pinnatipartite; corolla urceolate, 9-10 mm long, yellowishwhite when fresh; stamens exserted, staminode shorter than stamens; style 8 mm long...................... S. longiflora

1a. Leaves broadly ovate to circular to triangular or rhombic to deltoid, serrate to dentate; corolla ventricose, 5-7 mm long, purple when fresh; stamens included, staminode the same length as stamens; style 4-5 mm long......... S. nana