This is another western native, found along the west coast from Alaska to California and eastward only as far as Alberta and Wyoming. We have found it in several locations in Washington and in one location in British Columbia, a location that is in danger of being bulldozed for roadwork.
The plant can be quite small or quite large. We have seen them as small as 15 cm, seedlings perhaps, and as tall as 60 cm. The flowers, measured from the tips of the petals are about 12 cm across and about the same from the top of dorsal sepal to the bottom of the lateral sepal.
The literature says that each plant can have up to four flowers, but two is the most we have seen on any plant. We have not found them often, but when found they are often growing in profusion and a search will usually turn up more plants nearby.
They seem to prefer well-drained hillsides and the dappled shade of small trees and brush, making them somewhat hard to photograph. In one location we have found them on a very steep slope and in another with the brush so close that it was difficult to take pictures.
There is a form Cypripedium montanum fma. welchii which has a crimson border around the opening of the pouch. This form we have found and it seems quite common, but the green-flowered form we have not seen. There is also a hybrid this species and Cypripedium parviflorum, but that is a separate post.