Scientists Reveal Hidden Diversity in Brazil’s Iconic National Tree

A study by Linda Neaves and colleagues, published in the American Journal of Botany, combines genetic analysis and leaf measurements to uncover cryptic lineages in Paubrasilia echinata, known locally as pau-brasil or Brazilwood. This research offers new information about pau-brasil, a culturally important tree in Brazil but endangered in the wild

The study found five genetically distinct groups of pau-brasil, not just the three varieties previously recognised based on leaf size. Two groups matched up with rare large- and medium-sized leaf types, but the common small-leaved form split into three lineages. Leaf size varied 35-fold but did not neatly match genetic patterns, showing cryptic diversity. 

Pau-brasil inhabits Brazil’s Atlantic Forest, which is highly fragmented. Previously exploitation for its red dye made it endangered. The name comes from the Portuguese word for embers, referring to the red heartwood historically used to make red dye for textiles. This “brazilwood” gave Brazil its name and was a major export starting in the 16th century. Now pau-brasil is cultivated as an ornamental tree and source of wood for violin bows, but its wild diversity may not be protected.

Researchers collected samples across the tree’s range and analyzed genetic relationships using RAD-sequencing. They also measured leaf traits on herbarium specimens. Combining these approaches revealed the five genetic groups, which were related to geography and ecology more than leaf size. Neaves and colleagues write:

By combining morphological and genetic data from across the extant distribution of Paubrasilia echinata, we found evidence for at least five genetically distinct lineages within the fragmented Atlantic Forest of Brazil. These genetic lineages are highly geographically structured, and while some appear to correspond to the previously defined “Laranja”, “Café”, and “Arruda” leaflet morphotypes, individuals from northern Brazil were found to have leaf traits that overlap with both the “Café” and “Arruda” morphotypes. Further investigation into the morphological differences amongst sub-populations of P. echinata should refrain from using the three traditionally defined morphotypes related to leaflet size, but rather focus on maximizing conservation of all five lineages detected in this study. 

Neaves et al. 2023

The findings suggest cultivated pau-brasil trees represent limited genetic diversity. More populations should be protected to conserve this cultural icon, especially the rarest southern forms not currently in reserves. Understanding evolutionary relationships and functional diversity will aid the conservation of the species and the Atlantic Forest. Neaves and colleagues conclude:

The two lineages in most urgent need of further research and conservation are the rarer and less well-known “Café” and “Laranja” groups, that represent distinct evolutionary lineages and occur in different types of forests than the other populations. Whether these morphotypes should be formally recognised as distinct infraspecific taxa is an ongoing question. More work is needed on the “Laranja” morphotype to understand how widespread this apparently rare genetic lineage is, and whether hybridization with a second evolutionary lineage from Bahia is a natural phenomenon or the result of human introduction of different genotypes of P. echinata across the geographical range of the species. A better understanding of the original source of individual cultivatedtrees in urban environments and cacao plantations, and their relationship to wild specimens from fragmented populations, will help to guide conservation strategies for Pau Brasil.

Neaves et al. 2023

READ THE ARTICLE
Rees, M., Neaves, L.E., Lewis, G.P., de Lima, H.C. and Gagnon, E. (2023) “Phylogenomic and morphological data reveal hidden patterns of diversity in the national tree of Brazil, Paubrasilia echinate,” American Journal of Botany. Available at: https://doi.org/10.1002/ajb2.16241.

Cover: Brazilwood rare tree legumens, Sao Paulo. Image: Mauroguanandi / Wikimedia Commons.