Carapa guianensis is a widespread Neotropical tree species that produces a seed adapted for water dispersal. We conducted a pilot study of chloroplast DNA (cpDNA) variation in order to investigate the consequences of hydrochory on genetic diversity and geographic population structure in the lower Amazon basin. A survey of cpDNA haplotype variation reveals a strong regional structure, which suggests limited gene flow by seeds. Within site variation was detected only in one floodplain forest (varzea), suggesting that seed dispersal by water in these forests has the potential to mix maternal lineages. Several phylogeographic hypotheses are discussed with respect to these data.

Phylogeographic patterns of endemic species are critical keys to understand its adaptation to future climate change. Herein, based on chloroplast DNA, we analyzed the genetic diversity of two endemic and endangered tree species from the Brazilian savanna and Atlantic forest (Eremanthus erythropappus and Eremanthus incanus). We also applied the climate-based ecological niche modeling (ENM) to evaluate the impact of the Quaternary climate (last glacial maximum * 21 kyr BP (thousand years before present) and Mid-Holocene * 6 kyr BP) on the current haplotype distribution. Moreover, we modeled the potential effect of future climate change on the species distribution in 2070 for the most optimistic and pessimistic scenarios. One primer/enzyme combination (SFM/HinfI) revealed polymorphism with very low haplotype diversity, showing only three different haplotypes. The haplotype 1 has very low frequency and it was classified as the oldest, diverging from six mutations from the haplotypes 2 and 3. The E. erythropappus populations are structured and differ genetically according to the areas of occurrence. In general, the populations located in the north region are genetically different from those located in the center-south. No genetic structuring was observed for E. incanus. The ENM revealed a large distribution during the past and a severe decrease in geographic distribution of E. erythropappus and E. incanus from the LGM until present and predicts a drastic decline in suitable areas in the future. This reduction may homogenize the genetic diversity and compromise a relevant role of these species on infiltration of groundwater.