AimFunctional traits shape the distribution of taxa across environments. However, it remains unclear whether trait and environmental niche evolution are correlated, and what happened first: trait change facilitating environment shifts (pre‐adaptation) or environmental change leading to trait change (adaptation). We focus on a species‐rich Neotropical legume radiation to shed light on this enigma.LocationNeotropics.Time PeriodCenozoic.Major Taxa StudiedFabaceae: Papilionoidae: Swartzia.MethodsWe assembled leaflet, fruit and petal size data from monographs and herbarium collections for 86 to 96% of the c. 180 Swartzia species, inferred a dated Swartzia phylogenetic tree from existing DNA sequences covering 38% of the species and integrated these with distribution, soil and climate data. We used phylogenetic linear regression to quantify trait–environment relationships and applied comparative methods to evaluate modes of correlated evolution between traits and environments.ResultsLeaflet and petal size were strongly linked to climate, while fruit size was not associated with climate or soil characteristics. Evolutionary transitions to relatively low rainfall and low temperature environments were conditional on the evolution of small leaflets, whereas transitions to wet and warm environments were preceded by the evolution of larger leaflets. In contrast, transitions to the warmest or coldest environments were followed, rather than preceded, by petal loss.Main ConclusionOur results show that the macroevolution of functional traits has influenced the broad‐scale distribution of Swartzia across Neotropical rainforest, seasonally dry, montane and inundated habitats. We suggest that trait evolution is conditional on environmental change but both pre‐adaptive and adaptive processes may occur. These processes are important to understand the distribution of diversity at both regional (e.g. Amazonia) and global biogeographical scales.

Dicorynia stands out among the 17 genera of the diverse legume subfamily Dialioideae as an example of extreme floral reduction and specialization. It has asymmetric flowers presenting a heteromorphic calyx, trimerous corolla, and pair of highly dimorphic stamens, with one or both anthers polysporangiate. The two species of Dicorynia are Amazonian trees, one of which is highly valued for its timber. Despite the economic importance of the genus and an abundance of new collections, no comprehensive taxonomic study of Dicorynia has been completed since the publication of Koeppen’s monograph almost six decades ago, in which two species were recognized, one of which divided into six varieties. The present work employs integrative analysis of geographical, ecological, and extensive specimen-based morphological data to test previous delimitations of species and varieties. A new classification is adopted in an updated and comprehensive taxonomic revision of Dicorynia. We maintain two morphologically distinct and geographically separated species, D. guianensis and D. paraensis. The former is restricted to portions of the Guiana Shield north of the Amazon basin. At the same time, the latter is broadly distributed in the Amazon basin, but mainly north of the Amazon River. We recognize several taxonomically significant entities within the latter species, which, because they display limited morphological overlap and substantial geographical sympatry, we treat as varieties. However, we reduce the number of varieties from six to four. The taxonomic treatment contains new descriptions and illustrations, distribution maps, including two new areas of occurrence, conservation status assessments for all treated taxa, and identification keys to distinguish them. Nomenclatural, biogeographical, and ecological comments, including two new lectotypifications, are provided.