American Hydrangea Society
- Dedicated to the study of the genus, species and cultivars, as well as culture, habits, and hardiness. Event schedule, new introductions, photographs and resources.
- http://www.americanhydrangeasociety.org/

International Oleander Society
- Dedicated to the promotion of the Oleander in culture, history and lore features articles and membership information.
- http://www.oleander.org

The Rhododendron, Camellia & Magnolia Group of the Royal Horticultural Society
- Information on membership, events, publications, and seed exchange, and for each of the plant groups an overview of cultivation information, species, and hybrids, with photo gallery.
- http://www.rhodogroup-rhs.org/

Holly Society of America, Inc.
- Society for people interested in hollies, including both novices and skilled growers, to exchange information through scientific studies, publications, meetings, visiting holly collections, and other educational activities. Includes information about vari
- http://www.hollysocam.org/

The American Boxwood Society
- Not-for-profit membership organization devoted to the appreciation, scientific understanding, and propagation of the genus Buxus.
- http://www.boxwoodsociety.org

Azalea Society of America
- Gives information about azaleas, "the royalty of the garden". There are azaleas for almost any growing situation you have, with almost any color, habit and height you desire
- http://www.azaleas.org/