University of Vermont Extension 
Department of Plant and Soil Science

An Illustrated Encyclopedia of Clematis
Mary Toomey and Everett Leeds.  2001.  Timber Press.  428 pp, hardcover
Other than gardens in hot climates (this genus prefers cool), Clematis have a vast range of species and cultivars, varying in hardiness, but with at least some for most gardens.  This extensive reference covers over 550 selections, with 652 color photos.  The first part of the book is a thorough yet quite readable coverage of clematis history and culture.  Illustrations show plant parts and culture, photos show design possibilities. The second part is an A to Z listing of selections, with descriptions and cultural specifics for each.  At the end are several appendices, such as clematis by groups and by flower color.  For home gardeners and commercial growers alike of this genus, this is a valuable reference.

Plant listings include synonyms, origin, parents if a hybrid, habit, height, description, pruning group (if you're not familiar with this genus, depending on habit and flowering, they should be pruned at different times), flowering period, recommended use, and hardiness.  Close-up photos of flowers are quite inspirational as well representative and a great aid to identification.

Mary Toomey gardens in Ireland, and draws from her over 30 years growing this genus.  She is a PhD trained biologist, botanist, entomologist and soil ecologist, so brings this background to this genus but in a practical and easily digestible prose.  Everett Leeds grows clematis in Surrey, England and helped found several clematis societies.  Even though these authors are from the U.K.,  this book is quite appropriate for American gardens and gardeners.

In an interview, Mary Toomey describes why roses and clematis are often found together in gardens.  "...these two make no only good companions but also companionable plants.  As companionable plants, roses and clematis love each other, because one can weave its way through the other.  Therefore, when the roses are no longer "paying the rent" so to speak, clematis can be planted to take over that place, where they flaunt their flowers."