The infraspecific taxonomy of wild Anacardium occidentale is little studied. We investigated
whether wild populations on coastal dunes in Piauı, Brazil differed from non-wild populations.
Ten populations were sampled and twenty one morphological variables were measured.
Variation within and between populations was investigated with univariate and
multivariate statistics. Dune populations were mostly more similar to one another than to
domesticated ones. There was significant correlation between inter-population geographical
distance and morphological dissimilarity. Classification methods showed 96.4% successful
assignment to the dune category and 86% to 100% to dune populations
individually, but dune and non-dune populations overlap morphologically. Dune populations
had shorter, broader leaves, shorter drupes and fewer secondary veins. Non-dune coastal
populations showed strongest similarity to dune populations. Populations distant from the
coast were most divergent. The population from the cerrado region was most distinct, with
thicker leaf blades and narrower petioles. The dune populations are recognised as the
“restinga ecotype” of A. occidentale. Correlation of dissimilarity and distance may result
from gene flow and/or non-inherited environmental effects. Ecology and nomenclature (including
the vernacular “cajuı”) of the restinga ecotype are reviewed. Further comparison of
restinga populations is needed along the Brazilian coastline and with natural cerrado populations.