Rhipsalis, the largest genus of tribe Rhipsalideae (Cactaceae), comprises 37 characteristically epiphytic species and a few rupicolous ones. It is well represented in the Brazilian flora, and its center of diversity is in wet tropical and subtropical forests of southeastern Brazil. Rhipsalis dissimilis (G.A. Lindberg) forma epiphyllanthoides and R. floccosa (L.) subspecies pulvinigera are sister species with very distinct habits within the genus. This study analyzes and compares the morphoanatomy of these species aiming to verify which modifications found in the former may be related to its (rupicolous) terrestrial habit. We collected 23 individuals of R. dissimilis in an area of rocky outcrops in Ponta Grossa, State of Parana, and 23 individuals of R. floccosa in a remnant of Atlantic Forest formation in Curitiba, State of Parana. Length, diameter, area, volume, dry and fresh mass, water content, and stomatal and areolar density in the median portion of the stems of both species were measured. Histological slides were mounted to assess tissue thickness and percentage of lignified tissues. Both species present features typical of Cactaceae. Regarding habit differences, R. floccosa subspecies pulvinigera shows significant reductions of some tissues such as absence of ribs and diminished succulence, which constitute selected adaptations to epiphytism. Rhipsalis dissimilis forma epiphyllanthoides presents increased succulence, a lower height/diameter ratio, and ribs, among others. Such features are in line with those observed in other lineages of terrestrial cacti. Considering that Rhipsalis ancestral habitat was epiphytic, R. dissimilis may have retained a more plesiomorphic form suitable for colonizing a terrestrial habitat.
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