Also known as Franklin's Lady's Slipper, Cypripedium passerinum, though not the showiest, is the daintiest and most delicate of our native Lady's Slippers, as the name "Sparrow's-egg" suggests. It is also one of the rarer Slippers, found only in the north and there only in specific locations. The USDA lists it as being found across Canada but only in Alaska and Montana in the United States.
The plants are taller than the Large Yellow Lady's Slipper or the Mountain Lady's Slipper, and the flowers relatively small in comparison. The plants we have seen have been as much as 45-50 cm tall and the flowers about 10 cm tall with a lip that is quite large in proportion to the plant.
In the areas we have seen them they are always growing in and around scrubby trees, partially shaded from the full sun. They have also been in areas that are quite moist, such as the shore of a lake or a riverbank. We have found them growing mixed with Cypripedium parviflorum and Amerorchis rotundifolia.
There is said to be a dwarf form and we may have seen it, though it simply looks like a miniature version of the species. We think that it was the dwarf form because it was blooming when the larger forms were all finished. There is as well as a form with a pinkish pouch, but we have not seen it. Nor have we ever seen more than one flower on a plant, though it is suggested that they sometimes have two flowers.