Abstract
Summary The description of a new species of Oxalis sect. Rhombifoliae (R.Knuth) Lourteig from the state of Oaxaca, in Mexico is presented. To date, this section includes six species, of which four are American and two are from the Marquesas Islands, in French Polynesia. The new species belongs to a group of three, morphologically similar, species inhabiting areas ranging from northern Mexico to Guatemala: Oxalis clematodes Donn.Sm., O. madrensis S.Watson and O. yalinensis sp. nov., the latter of which is described here. These three species are compared morphologically and their geographic distributions are illustrated. The new species differs from the other two mostly by the obcordate leaflets and the inflorescences with shorter peduncles and bracts. This manuscript also includes a preliminary conservation assessment of O. yalinensis based on IUCN guidelines.