Cypripedium x columbianum, the Columbia Hybrid Lady's Slipper, is a natural hybrid of Cypripedium parviflorum, the Yellow Lady's Slipper, and Cypripedium montanum, the Mountain Lady's Slipper. When found it is often growing with one or both parents. In an undisclosed location in Washington there is a population of well over one hundred plants that includes this hybrid. In fact, I am putting all the plants found at this location under this name since it is doubtful that any of them are pure Cypripedium parviflorum or montanum, though some of the flowers look like one or the other parent. The flowers that are clearly hybrids have neither the white lip of Cypripedium montanum, nor the yellow lip of Cypripedium parviflorum but range in the color of the lip from off white through ivory to pale yellow.
flowers that look like Cypripedium parviflorum
flowers that are clearly Cypripedium x columbianum