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 'Grandiflorus'.
NARGS Image Gallery - Photograph(s) contributed by North American Rock Garden Society members. (1 photo)
Plant Delights Nursery - Catalog page with photo, horticultural basics, and descriptive blurb. (additional pages for other varieties) (1 photo)
Rob's Plants - Plant profile with basic horticultural information and often personal observations. Also seed germination records. (zone 3-8) (5 photos)