Polar Disjunctions

This chapter deals with taxa whose ranges of occurrence are disjunct between the Northern and Southern Hemispheres. Some of the examples involve taxa with related members whose distributions lit into other categories, some of which have been discussed above. Chrysosplenium, for example, has a distribution that involves disjunctions between Asia and North America, between eastern and western North America, and between the Northern Hemisphere and the Southern Hemisphere. 

Excellent general information on amphitropical relationships involving taxa from the Pacific Coast of North America and South America appears in a symposium on the subject published in the 1963 Quarterly Review of Biology (Raven, 1963) with contributions from Lincoln Constance on Apiaceae, Larry Heckard on Hydrophyllaceae, Kenton Chambers and Robert Omduff on genera in Asteraceae, and Peter Raven on an overview of floristic relationships between North America and South America. 

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