A synopsis of Christiana DC. (Malvaceae, Brownlowioideae), with a new species from the Brazilian Atlantic Forest

A taxonomic synopsis is provided for the genus <i>Christiana</i>, with emphasis on the American species. Full synonymies, typifications, comments about distribution, and notes on main diagnostic characteristics, as well as conservation status and phenology, are provided. We describe a new species, <i>C.restingae</i> T.S. Cout., Barb.Silva & Dorr, <b>sp. nov</b>. With this addition, <i>Christiana</i> now comprises six species, with its center of richness in South America, where five species occur. The new species is endemic to Brazil where it is known only from Atlantic Forest and Restinga in the states of Espírito Santo and Rio de Janeiro, and is preliminarily assessed as Critically Endangered. Illustrations, images, a distribution map, SEM images of vegetative and reproductive structures, taxonomic comments, and information about the ecology and conservation of <i>C.restingae</i> are provided. Furthermore, the distribution and introduction of <i>C.africana</i> in the Americas is discussed. A total of eight names of <i>Christiana</i> species or synonyms described in four other genera (<i>Berrya</i>, <i>Carpodiptera</i>, <i>Entelea</i>, and <i>Speirostyla</i>) are lectotypified.