About.com - A Tree Leaf Key
A quick leaf guide for identification of over 50 common North American trees.
Bartosz Pacula's Pictures of Trees
Large photo gallery of cultivated and wild trees in Europe.
Basics of Tree ID
A basic guide to identifying trees. Describes leaves, fruits, barks, with many images.
Dendrology at Virginia Tech
Includes ID keys and fact sheets on over 450 species of wild and cultivated trees in the eastern USA.
Fact Sheets for 680 Trees
Descriptions, illustrations, US range maps, and cultivation of cultivated species from around the world.
Foliage Identification Test
An interactive guide to identifying trees and shrubs of Ontario. Image intensive.
Introduction to Tree Identification
A resource for beginners and others. Includes a collection of descriptive graphics showing leaves, and buds, with notes.
Palm Tree Photo Gallery
Over a thousand photographs of palms from around the world.
Plant Kaleidoscope
Large image gallery of cultivated woody plants in Europe.
SelecTree for California
A tree database for California. Includes non native trees.
Taxonomy of Woody Plants
Links on woody plant taxonomy including original identification keys to major genera.
Twig Identification Test
Interactive identification of leafless twigs and axillary buds. For the trees and shrubs of Ontario.
What Tree is it?
Tree identification. Especially useful way to work from the shapes of leaves.