A new Philippine species of Ridsdalea (Rubiaceae, Ixoroideae) from karst vegetation in Palawan

Ridsdalea philippinensis (Rubiaceae), a new species from the karst forest in El Nido (Palawan, Philippines), is described and illustrated. It is unique among Malesian Ridsdalea species in having a corolla tube that is distinctly inflated at the apex, a character state also displayed by R. sootepensis and R. thailandica from Laos and Thailand. Amongst others, R. philippinensis, however, differs from both of these species in having smaller flowers and anthers that do not emerge from the corolla tube. An updated key for Philippine Ridsdalea is also presente