The Hydrophyllaceae

The Hydrophylalceae, a predominantly North American family, presents four cases of amphitropical distribution. Two of these (Nama dichotomum and the Phacelia magellanica complex) have apparently reached South America by a stepwise migration along the mountain systems which partially connect the temperate regions of the two continents. These groups still inhabit the mountains of southern Mexico and the northern Andes. Greater distances separate the other two amphitropical groups (Phacelia crenulata group and Phacelia sect. Euglypta), making chance, long-distance dispersal to the south a likely explanation of their distributions. No conspicuous adaptation for dispersal exists in any of these groups, except for the hispid capsule and adherent calyx in the Phacelia magellanica group, which would aid in dispersal by animals. Within the Phacelia magellanica group it appears likely that only one North American species migrated to South America, although there are now at least eight recognizable taxa there, including one rather advanced annual species, P. simplicifolia. F hybrids of low fertility have been obtained in the complex between two species of Chile and two species of California.