XVI International Botanical Congess

Larrea is a common desert shrub, with an amphitropical distribution covering arid regions of South America and North America. There are 4 species present in South America, L.ameghnoi and L.nitida in northern Patagonia, L.cuneifolia in western Argentina and L.divarcata in semi- arid regions of Argentina. One species is found in North America, L.tridentata, which has three different ploidy levels (2x,4x,6x). The evolutionary history of the genus Larrea was assessed by determining patterns of genetic variation using Intersimple Sequence Repeats (ISSR). The phylogenetic relationships were generally congruent with morphological studies, however there were notable differences in L. nitida. We have also documented variation between and within ploidy levels of North American Larrea.