In The Gardener's Guide to Growing Clematis, Raymond Evison, world authority on clematis, provides a fresh look at the genus by focusing on not just the popular large-flowered cultivars but also the less-well-known species and their varieties. The sheer range of flower types from the large and flamboyant hybrids through to the delicate bell-shaped species means that there is a clematis for every situation and effect. A comprehensive plant directory provides detailed and authoritative descriptions of around 375 species and varieties.
The Gardener’s Guide to Growing Clematis by Raymond J. Evison (Timber Press Inc. 1998)(635.93334). This is an excellent guide to the culture and the various species of clematis. My rating: 7.5/10, finished 2002.