The Rio Mayo region of northwestern Mexico is a major geographic area whose natural history remains poorly known to outsiders. Lying in a region where desert and tropical, northern and southern, and continental and coastal species converge, it boasts an abundance of flora first documented by Howard Scott Gentry in 1942 in a book now widely regarded as a classic of botanical literature. This new book updates and amends Gentry's Rio Mayo Plants. Undertaken with Gentry's support and participation before his death in 1993, it reproduces the original text, which appears here with...