Geographic isolation alone does not explain divergence of a group of orchid species across Brazil’s campos rupestres sky-islands

Mountains play a crucial role in the origin and maintenance of Neotropical
biodiversity, but there are still unanswered questions about the
diversification of the campos rupestres (CR), an herbaceous-shrubby
sky-island vegetation in Eastern South America. For orchids distributed
across this disjunct rock habitat, difficulties with distinguishing
morphological taxa add an additional challenge to disentangling the
history of divergence. Here, we combined the power of ddRAD genomic data
with broad sampling of Bulbophyllum sect. Didactyle (Orchidaceae), across
the CR and other Neotropical outcrops, to estimate evolutionary
relationships and reconstruct the biogeography of the group’s
diversification. Although genetic lineages generally align with geographic
disjunctions, we also observe distantly related lineages within some
previously recognized species. For such taxa, their lack of monophyly and
a shared regional divergence pattern suggests a complex history that may
include unrecognized diversity. When viewed through the lens of
morphological variability, our study raises intriguing questions about the
persistence and permeability of species barriers among orchid populations.
These results, in addition to the recency of the divergence history of B.
sect. Didactyle, provide insights about hypothesized community level
versus species-specific paths of diversification across the Neotropical
sky-islands of the CR.