Abstract
Plant taxonomy is primarily based on patterns of morphological variation and geographical distribution. Plant-parasite relationships can also offer clues regarding the phylogeny of the host plant. Many obligate parasites coevolve with their hosts, eventually becoming restricted to an individual taxon. Host restriction may take place at different taxonomic ranks, i.e., parasites may become restricted to one host genus within a plant family, to one species within a genus, or to one infraspecific taxon within a species. This phylogenetic congruence between plants and their parasites may be due to cospeciation or due to co-adaptation (reciprocal adaptive selection). Our study reviewed plant-parasite interactions with regard to putative Cannabis taxa. The results Curators of the following herbaria are thanked for loaning collections: BPI, IMI, FH, GH, BR, ILLS, MICH, VT. suggest that certain parasites may have co-evolved with putative species and biotypes within the Cannabisgenus.