Insights into long-distance dispersal and ecological and morphological evolution in the fern genusMicrogrammafrom phylogenetic inference

Abstract

The epiphytic fern genus Microgramma (Polypodiaceae) comprises 30 species occurring mainly in the Neotropics, but with one species in Africa, an example of trans-Atlantic disjunction. Morphologically and ecologically, Microgramma presents a wide range of variation that is not seen in the most closely related genera. Recent studies have changed the circumscription of Microgramma to better conform with phylogenetic evidence, but no comprehensively sampled study has addressed the evolution of this lineage. The present study aimed to investigate phylogenetic relationships, ecology and morphological evolution and to test the role of long-distance dispersal in Microgramnza. 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 previously proposed infrageneric classification system. Several morphological traits appear to be homoplastic, including leaf dimorphism. Tuber-like myrmecodomatia are suggested to be synapomorphic for one lade, although ant-plant associations appear in two lineages. Microgramma lycopodioides in the Neotropics and M. mauritiana in Africa, once thought to be conspecific, are not closely related, with the African species nested in an Atlantic Forest Glade, indicating a long-distance dispersal event estimated to have occurred c. 15 Mya from South America to Africa, followed by speciation.