Three new species of Ageratina subg. Neogreenella are described from Mexico, as follows: Ageratina mayajana, from Mpio. San Miguel Chimalapa, Oaxaca; Ageratina mazatecana, from Mpio. Santa Maria Chilchotla, Oaxaca; and Ageratina pochutlana from Districto Pochutla, Oaxaca. Although all of the taxa belong to the A. subg. Neogreenella, only the latter two relate to the A. mairetiana complex as defined by Turner (1987, 1997). A revised key to that complex is provided.