Cypripedium Sabine var. alba?
This cross combines the two large flowering species C. macranthos and C. fasciolatum. This cross was made with a yellowish fascilatum and a white C. macranthos - The first flowering plants are mostly flowering pure white - only 20 percent has been flowering as a very beautiful semialba form. So you will have a win win situation. PH 6,5 / Goc 5a + 5 b / hs - sch