Cactus exhibit perfection in both form and function. It is hard to imagine anything you could design that is adapted so perfectly to its environment than a cactus and at the same time has such a perfection of form and beauty. Frank Lloyd Wright implemented a movement called Organic Architecture. This is defined as a philosophy of architecture
which promotes harmony between human habitation and the natural world
through design approaches so sympathetic and well integrated with its
site that buildings, furnishings, and surroundings become part of a
unified, interrelated composition. See Wikipedia:Organic Architecture. If you apply this definition to this prickly pear cactus, you can see why I think they are perfect examples.