Passiflora tacanensis, a new species from southern Mexico, is described and illustrated. It was discovered during the course of a taxonomic revision of Passiflora subgenus Decaloba supersection Cieca and is assigned to that group of apetalous passion flowers. Passiflora tacanensis is known only from one fruiting herbarium specimen that was collected in southern Mexico on Volcán Tacaná in a high mesophytic forest. It is distinguished from its closest relatives, P. coriacea, P. sexocellata, P. mcvaughiana, and P. xiikzodz, by its foliose stipules, leaves that lack laminar nectaries but possess petiolar nectaries, and wide seeds with a chalazal beak that is not well developed.