Mikael Hedrén published this absolutely drop-dead gorgeous new species, known only from central Somalia, in 1993. Its closest relative is probably Ruellia discifolia that, unlike R. nocturna, is much more widespread in tropical areas of northeast Africa. The two species differ primarily in calyx morphology, with lobes of R. nocturna being conspicuously connate. Don’t believe me? See the photo for yourself. Simply spectacular… you’ll want to invite it over for a glass of wine.
My educated guess: R. nocturna and R. discifolia are sister species, together with R. carnea. Oh, and somewhere in the mix is R. insignis. Times are tough in Old World Ruellia. Don’t give up.
Wild collected, Somalia, photo of holotype (Thulin, Hedrén, & Dahir #7380) at Uppsala.