Adiantopsis alata was described by Prantl in 1883 and was distinguished from A. radiata based on the presence of large adaxial carinae along the stipes. Morphological and molecular analyses of specimens meeting this general description reveal four distinct species, with one endemic to eastern Brazil and three others restricted to the Guiana Shield. The syntypes for A. alata represent two different species, one from Brazil and the other from Guyana. Here, we designate a Brazilian syntype as the lectotype for A. alata and describe and illustrate three new palmate species from the Guiana Shield with adaxial carinae along their stipes: A. aurea, A. hickeyi, and A. scalariformis. A distribution map for the new species and a key to all ten palmate members of Adiantopsis are provided.