How about:
Cypripedium reginae Walter f.
albolabium Fernald & B.G.Schub ?
But I would be inclined to go for simply:
Cypripedium reginae v.
album Although one's natural inclination may be to call it Cypripedium reginae v. alba, that would be incorrect as the varietal epithet takes its gender from the genus, which in this case is -
um = neuter, hence alb
um. - How I enjoyed my nine years of Latin at school
If in doubt, I tend to consult the International Plant Name Index, maintained by Kew:
http://www.ipni.org/ipni/plantnamesearchpage.doTo find the above result I entered: Genus: Cypripedium, Species: reginae.
