DISTRIBUTION OF SPONTANEOUS PLANT HYBRIDS

Natural hybridization is a relatively common feature of vascular plant species and has been demonstrated to have played an important role in their evolution. Nonetheless, it is not clear whether spontaneous hyb ridization occurs as a general feature of all plant families and gener a or whether certain groups are especially prone to spontaneous hybrid ization. Therefore, we inspected five modern biosystematic floras to s urvey the frequency and taxonomic distribution of spontaneous hybrids, We found spontaneous hybridization to be nonrandomly distributed amon g taxa, concentrated in certain families and certain genera, often at a frequency out of proportion to the size of the family or genus, Most of these groups were primarily outcrossing perennials with reproducti ve modes that stabilized hybridity such as agamospermy, vegetative spr ead, or permanent odd polyploidy. These data suggest that certain phyl ogenetic groups are biologically predisposed for the formation and mai ntenance of hybrids.