Insights into long-distance dispersal and ecological and morphological evolution in the fern genus Microgramma from phylogenetic inference

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.

Automated summary

The epiphytic fern genus Microgramma, mainly found in the Neotropics, displays a wide range of variation in morphology and ecology not seen in closely related genera. Recent studies have revised the circumscription of Microgramma based on phylogenetic evidence, leading to the identification of five clades that do not align with previous infrageneric classification systems. Homoplastic traits, including leaf dimorphism, are found within the genus, along with ant-plant associations in two lineages, suggesting complex evolutionary patterns. Long-distance dispersal events are hypothesized to explain the distribution of certain species, such as Microgramma lycopodioides in the Neotropics and M. mauritiana in Africa, highlighting the importance of biogeography in the evolution of this lineage.