Systematics of Pipevines: Combining Morphological and Fast‐Evolving Molecular Characters to Investigate the Relationships within Subfamily Aristolochioideae (Aristolochiaceae)

A combined phylogenetic analysis of the Aristolochioideae was conducted based on 72 morphological characters and molecular data sets (matK gene, trnK intron, trnL intron, trnL-trnF spacer). The analysis sampled 33 species as the ingroup, including two species of Thottea, 30 species of Aristolochia, and the monotypic genus Euglypha, which represent all the infrageneric taxa formally described; Saruma henryi and Asarum caudatum were used as the outgroup. The results corroborate a sister-group relationship between Thottea and Aristolochia and the paraphyly of Aristolochia with respect to Euglypha, which consequently should be included in Aristolochia. Two of the three subgenera within Aristolochia (Isotrema and Pararistolochia) are shown to be monophyletic, whereas the signal obtained from the different data sets about the relationships within subgenus Aristolochia is low and conflicting, resulting in collapsed or unsupported branches. The relationship between the New World and the Old World species of subgenus Aristolochia is conflictive because morphological data support these two groups as monophyletic, whereas molecular data show the monophyletic Old World species of Aristolochia nested within the New World species. A sister-group relationship is proposed between Aristolochia lindneri and pentandrous species, which suggests that a group of five species from central and southern South America (including A. lindneri) could be monophyletic and sister to Aristolochia subsect. Pentandrae, a monophyletic taxon consisting of ca. 35 species from the southern United States, Mesoamerica, and the West Indies.