Anthurium bromelicola and A. sterilispadix (Araceae): two distinct bromeliad commensals with highly unusual inflorescence morphology endemic to Northeast Brazil

Anthurium sterilispadix (previously A. bromelicola subsp. bahiense ) is recognized as a new species, closely related to A. bromelicola and representing a third species of Araceae exhibiting commensalism with Bromeliaceae. The two species share the same highly unusual slender twining habit but differ markedly in inflorescence morphology, each exhibiting characteristics unique in the genus and suggesting divergent pollination biology. In A. sterilispadix , the spathe spreads widely without differentiation into tube and lamina, the lamina is smooth and pink adaxially showing colour changes according to the stage of anthesis and the greater part of the narrowly tapering pale yellow spadix consists of modified sterile flowers which appear to be osmophoric. In A. bromelicola the spathe has tube-blade dimorphism, is adaxially deep purple and conspicuously ribbed, the spadix is relatively stout and the flowers have black-purple tepals and are all fertile. Anatomical study of leaves and inflorescences of both species revealed unusual features for the genus, such as the presence of vascularized ribs in the A. bromelicola spathe, and sterile osmophoric regions in the A. sterilispadix spadix; these novel characters are documented and discussed for the first time here. Nomenclature, taxonomic descriptions, images, geographical and ecological notes and an identification key are presented. Both species are endemic to the Brazilian Atlantic Forest region and are estimated to be endangered.