The Santa Ana River is the largest watercourse in the heavily populated coastal plain of southern California. Despite the encroachment of urban development, the river and its environs are home to nearly 1,400 plant species.

In this seminal guide to the flora of the Santa Ana River, Oscar F. Clarke and his team have compiled descriptions of 900 plant species, accompanied by 3,200 images and illustrations. The book also serves as an introduction to basic botanical concepts and is arranged by evolutionary relationships, to aid readers in plant identification. Historical and cultural uses, plant diseases, and associations with insects, birds, and mammals of both native and introduced species are woven together with technical information to paint a rich picture of the flora of this region as well as to relate it to that of the rest of the world.