What is the name of this popular orchid?

Cypripedium parviflorum, commonly known as Yellow Lady's Slipper, is found across virtually all of the United States and Canada, from Alaska to Georgia. It is a widely variable species, with four varieties and multiple hybrids, making identification and delimitation difficult. It produces a large flower with a pale to dark yellow pouch-like labellum, which sometimes has reddish spots on the interior.