A new phytoptid genus and two new species, Solenocristus karooensis n. g. & n. sp. and S. searsius n. sp. (Phytoptidae, Sierraphytoptinae, Sierraphytoptini), were collected in the Eastern and Western Cape provinces of South Africa, from southern African endemic dicotyledonous trees Schotia afra (Fabaceae) and Searsia lucida (Anacardiaceae) respectively. They are described and illustrated with the aid of conventional light microscopy and low temperature scanning electron microscopy. Females of both new species possess a distinct pregenital plate divided into two parts by a subcuticular medial ridge. Additionally, in S. karooensis n. sp. the movable digit of the male chelicerae varies in length: among six observed males, three males had a movable digit (md) twice shorter than the fixed digit (fd), in one male it was slightly shorter than fd and in the remaining two males md and fd were of the same length. An updated key to the world genera of the tribe Sierraphytoptini is given. The key incorporates data on seven sierraphytoptine genera including three genera (Neoprothrix Reis & Navia, Solenoplatilobus Chetverikov & Craemer and Solenocristus n. g.) which were described since the last generic key of Eriophyoidea by Amrine et al. (2003) was published.