All five Piperias (now Platantheras) can be found in Olympic National Park. We found four of the five when we were there in July, but this one, the fourth we found, was very nearly finished flowering. In fact, we found only one spike that still had any flowers on it and they were well on their way to oblivion. The species looks like Piperia unalascensis, the Alaskan Piperia, but has white instead of green flowers. The inflorescences grow to 60 cm with numerous 3-4 mm flowers. At flowering the leaves are usually withered away or starting to wither, a characteristic of all the Piperias. Known until recently as Piperia candida, it is now classified as Platanthera ephemerantha.
Along with Piperia candida we found more Piperia elongata, with its small, faintly fragrant, green flowers and long downward-curved spur. Like the other Piperias, it seems to be one of the few orchids unaffected by the hot dry summer we've had, though, as is characteristic, the leaves have usually withered away. These plants tend to grow on exposed hillsides, trailsides, and dry mossy banks, as well as in dry forests. Piperia elongata, now Platanthera elongata, is the last of the Piperias to bloom, though their blooming seasons overlap and it is possible to see them all in bloom at the same time. On this trip it was also the most common of the Piperias and seemed to be on every roadside bank.
Note: I've included some older pictures of Piperia candida for lack of anything recently taken.