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<div>The genus <i>Phytophthora</i> contains incredibly successful pathogens in both forest and agricultural ecosystems. <i>Phytophthora</i> species have long taken advantage of cultivated hosts to expand their geographic range. For example, genetic data indicate that early explorers may have spread <i>P. palmivora</i> around the world with coconuts. More recently, nursery stock has been implicated in the movement of multiple <i>Phytophthora</i> species, most notably the multiple introductions of <i>P. ramorum</i> leading to disease epidemics in wild and cultivated forests. Evolutionary changes in these pathogens are also likely to be responsible for their success upon introduction to new hosts and environments. Several <i>Phytophthora</i> pathogens exhibit high heterozygosity within genomes, which may contribute to their adaptive potential. Some of this intra-individual variation is due to polyploidy. We have found substantial triploidy or aneuploidy even in sexual populations of <i>P. infestans</i>. <i>Phytophthora </i>genomes may also exhibit high heterozygosity because they are interspecific hybrids. The tree pathogens <i>P. andina</i>, <i>P. alni</i>, and <i>P. palmivora</i> all exhibit high allelic variation within genomes due to interspecific hybridization. The relative stability of cultivated systems may provide the opportunity for the eventual success of otherwise high risk evolutionary genetic strategies in <i>Phytophthora</i> pathogens.</div>