Abstract
Dioon oaxacensis sp. nov. (Zamiaceae), a new cycad species from Oaxaca, Mexico, is described. The morphological traits of the new taxon are compared with its sister species, D. merolae. The species delimitation between the two species is consistent with previously published genetic evidence. Dioon oaxacensis can be easily identified by its flat, stiff, straight leaflets obliquely inserted to rachis, and by its large reproductive structures. Populations of D. oaxacensis usually occur in dry habitats, growing on rocky hillsides, and co-habiting with plants well recognized to be adapted to aridity.