BBC Gardening - Plant profile with horticultural details and garden uses. (1 photo)
Dave's Garden PlantFiles - Profile page with horticultural basics, and member-contributed photos and comments. (zone 5-9) (10 photos)
Denver Botanic Gardens - Description, native range, and cultural requirements. (additional pages for other varieties) (zone 5). Also a page for 'Alboplenum'.
Floridata - Illustrated informative profile page with notes on culture, usage, and noteworthy features. (zone 4-8) (2 photos)
Missouri Botanical Garden - Plantfinder page for one of the plants growing at the garden, with usually one or more photos, horticultural information, and noteworthy characteristics. (zone 4-8) (2 photos). Also a page for 'Pleniflorum'.
NARGS Image Gallery - Photograph(s) contributed by North American Rock Garden Society members. (2 photos)