Two new species of Marsdenia (Apocynaceae) from limestone outcrops in Brazil

Limestone outcrops often harbour floras rich in threatened and narrowly endemic species. Still, these formations, usually associated with karst landscapes, remain floristically poorly known, and so are often neglected in conservation programmes. In Brazil, three species of Marsdenia (Apocynaceae) endemic to limestone outcrops are known: M. breviramosa, M. virgultorum and M. zehntneri. In this work, we describe and illustrate two new species of Marsdenia restricted to karst landscapes: M. calcaria from the state of Minas Gerais and M.phallica from the state of Goias. We also include illustrations of M. zehntneri, the species morphologically most similar to the two new species, and in situ images of the species of Marsdenia from limestone formations in Brazil (except for M. virgultorum, which is known only from the type). A geographic distribution map and an identification key for the five species known from limestone formations are also provided.