A new species, Platanthera yosemitensis Colwell, Sheviak and P. Moore, from Mariposa County, California, is described and illustrated. Endemic to wet montane meadows between the main stem and the South Fork of the Merced River in Yosemite National Park, it is distinct from Platanthera stricta Lindl., P. sparsiflora (S. Wats.) Schlecter, and P. purpurascens (Rydb.) Sheviak \& W. F. Jennings based on vegetative habit, floral morphology, color, and fragrance and pollination mechanics.