Insights on long-distance dispersal, ecological and morphological evolution in the fern genus Microgramma from phylogenetic inferences

The epiphytic fern genus Microgramma (Polypodiaceae) comprises 30 species occurring mainly in the Neotropics with one species in Africa, being an example of trans-Atlantic disjunction. Morphologically and ecologically, Microgramma presents a wide variation that is not seen in its closest related genera. Recent works changed the circumscription of Microgramma to better conform with phylogenetic evidence, but no comprehensively sampled study has addressed the evolution of this lineage. This study aimed to investigate phylogenetic relationships, ecological and morphological evolution within Microgramma, as well as test the role of long-distant dispersal in the history of the genus. Sequences from five plastid regions were used to infer the phylogenetic relationships and estimate divergence times. Our results show five clades in Microgramma that do not corroborate any infrageneric classification system proposed. Several morphological traits seem to be homoplastic, such as leaf dimorphism. Tuber-like myrmecodomatia are suggested to be synapomorphic for one clade, although ant-plant association appears in two distinct lineages. Microgramma lycopodioides and M. mauritiana are not closely related, with the African species nested within an Atlantic Forest clade, indicating a long-distance dispersal event estimated to have occurred around 15 Ma from South America to Africa, followed by speciation.