Mathew Rees, Linda E. Neaves, Gwilym P. Lewis, Haroldo C. de Lima, Edeline Gagnon

Paubrasilia echinata (Lam.) Gagnon, H. C. Lima & G. P. Lewis ("Pau Brasil") is the national tree of Brazil, an endangered species endemic to the Brazilian Atlantic Forest. The wide distribution, spanning over 2000 km, matches extensive plasticity in leaf morphology. Three morphotypes are commonly identified based on leaf size but it is unclear if they represent distinct taxa or a single polymorphic species. This study aims to clarify the taxonomic position of the three morphotypes to inform conservation decisions. A morphometric study based on leaf characters of herbarium specimens was coupled with genetic analyses using genotype-by-sequencing data. We used maximum-likelihood and coalescent methods to evaluate the phylogenetic and population structure of the species. We compared these with a morphological dendrogram built from hierarchical clustering. We found that two of the three morphotypes formed separately evolving lineages, that the third morphotype formed two geographically separate lineages, and that northern trees with intermediate leaf morphology formed a separate fifth lineage. Leaflet size varied by over 35-fold and although morphological clustering generally matched the genetic patterns, there were some overlaps, highlighting the cryptic diversity within this group. Our genetic and morphological results provide some evidence that cultivated trees from different states in Brazil seem to be of limited genetic origin and do not reflect the broader genetic and geographical diversity of the species. This suggests that more care is needed to protect and preserve the overall genomic diversity of this endangered and iconic species. This article is protected by copyright. All rights reserved.