Biosystematic evidence for hybridization between Arctostaphylos nissenana and A. viscida

Arctostaphylos viscida Parry andA. nissenana Merriam were studied in Eldorado County, California, to check reports in the literature of hybridization between the two. Population samples were collected near Diamond Springs, where they occur sympatrically. A population sample of pureA. viscida, collected else-where, and miscellaneous herbarium specimens ofA. nissenana, were used for comparison. Data from analysis of six character differences, presented as pictorialized scatter diagrams and histograms, clearly indicate hybridization and back-crossing in the Diamond Springs populations; but we do not agree with Knight (1966) that theA. nissenana populations of this area are hybridized as a whole. Our data do not support Jepson’s (1939) opinion that the type ofA. nissenana may be of hybrid origin betweenA. viscida andA. nissenana var.arcana Jeps.