We have found it on almost every hiking trip and along the roadsides in every mountainous area of the Pacific Northwest, often by the thousands. Along the Yellowhead Highway in the mountains of British Columbia, for example, we have seen it blooming mile after mile in every marshy spot.
There are three varieties of this species, distinguished by the length of the spur, which probably indicates different pollinators for each. Var. albiflora has a spur shorter than the lip, var. dilatata a spur the length of the lip and var. leucostachys, a spur much longer than the lip.
The plants can be quite short, around 20 cm, but are often much taller, around 100 cm. The 2 cm flowers are crowded along the length of the stems in large numbers, often over 100 flowers per plant. We have noticed that quite often the lip catches in the dorsal sepal so that the flower does not open completely.
There are several natural hybrids of this species and its varieties with P. stricta and sparsifolia. These usually resemble P. dilatata, except for the flower color which is greenish, rather than pure white. The only one of these natural hybrids that we've seen has been sufficiently different to warrant a separate post.
This species also ranges from Alaska across Canada and the northern United States as far south as Pennsylvania and Indiana, California and New Mexico. Varieties albiflora and leucostachys, however, are more limited in range, and can be found only in the western United States and Canada.