Passiflora L. is the most important genus of the family Passifloraceae, native to tropical America, South-East Asia and Oceania. Mainly distributed in the neotropics, from coastal regions to elevations about 4,300 m, its 576 species have adapted to highly diverse environments and forged many strong interactions with animals (herbivory, mutualisms of pollination and protection), giving rise to a formidable species diversity through a particularly complex evolution and phylogeography. Since the first botanical explorations of the New World, taxonomical studies have faced considerable difficulties in interpreting this morphological diversity in terms of evolution, many traits showing lability and/or a wide dispersion throughout the genus. The last classification reduced the number of subgenera from 22 to 4 (Decaloba, Passiflora, Astrophea, and Deidamioides). The first three, corresponding to dominant ploidy levels (2n=12, 18, and 24 chromosomes, respectively), have been validated by molecular phylogenetic studies. The fourth, Deidamioides, has been divided in two clades, at least. Moreover, dioecious species formed a fifth subgenus, Tetrapathea. At lower levels, there remain many problems in the classification of species and the comprehension of their evolution with independent acquisitions of the same trait, cases of reticulate evolution, paternal or biparental inheritance of the chloroplast genome, as well as intraspecific or even intra-individual variability for certain gene sequences.