Molecular and morphological systematics of the 'tiger-flower' group (tribe Tigridieae: Iridaceae), biogeography and evidence for the adaptive radiation of the subtribe Tigridiinae

The tribe Tigridieae (Iridaceae) is strictly a New World group of plants with centers of diversity in temperate and Andean South America and Mexico. The tribe comprises plants with highly colored flowers that exhibit great morphological variation. Within the tribe, the taxonomic boundaries and phylogenetic relationships are confusing and need morphological and molecular cladistic analysis. Morphological variation, ITS and cpDNA nucleotide sequences were used separately and in combination to evaluate the phylogenetic relationships of the Tigridieae. The comparison of morphological results with the ITS phylogeny indicated that groups of species based strictly on floral morphology, with syndromes closely tied to pollinator attraction, may have included phylogenetically unrelated taxa as a result of floral convergence. The total evidence supported a monophyletic Tigridieae composed of two major lineages, the basal containing some members of subtribe Cipurinae (Calydorea, Cipura, Cypella and Nemastylis), the other containing the traditionally recognized subtribe Tigridiinae plus Cardiostigma, Nemastylis, Eleutherine and Ennealophus (Cipurinae). The Mexican-Guatemalan Tigridiinae was strongly supported as a monophyletic group that has undergone a recent radiation possibly triggered by palynological and ploidy changes and driven by plant-pollinator interactions. A graphical tree of trees analysis showed the morphological trees to be the most topologically distinct both within trees based on morphological data and among trees based on any data type. Finally, the cladistic analysis of the combined data set supported a recurrent migration of Cipurinae from South to North America and a South American origin of the Mexican-Guatemalan subtribe Tigridiinae.