New Ornamentals Society - http://members.tripod.com/~Hatch_L/nos.html Devoted to the study of new and rare ornamental landscape plants. Includes an online source guide and plant encyclopedia.
American Ivy Society - http://www.ivy.org/ A non-profit organization dedicated to preserving the genus Hedera through education and promotion. Site offers contact information, species photos with descriptions, a classification system, care instructions, article collection, membership details, and a question answering resource.
Passiflora Society International - http://www.passiflora.org/ Dedicated to the preservation, study, and dissemination of Passiflora.
The Geraniaceae Group - http://www.geocities.com/RainForest/Canopy/3139/ An international horticultural club interested in the species of all the genera of the Geraniaceae Family.
The International Geranium Society - http://www.intgeraniumsoc.com/ Society for the enjoyment of plants in the geraniaceae family centered in California. Events, information about membership and the magazine, culture tip sheets, and a photo gallery.
Hebe Society - http://www.hebesoc.org/ International society based in Britain promoting the cultivation and conservation of hebes and other New Zealand native plants. Includes plant profiles and photos, FAQs, and links.