Synonyms: Phlox diffusa ssp. diffusa, Phlox diffusa var. longistylis, Phlox diffusa ssp. longistylis
Spreading phlox is a beautiful, primarily mat-forming perennial. It may occasionally be found with upright growth, but not exceeding 10 cm in height. Its leaves are green, and not sticky or hairy. They tend to be much softer to the touch than those of many phloxes. Leaf shape is acicular or needle-like, with a length of 5 to 20 mm, and a width of 1 to 2 mm.
The flowers are solitary and nearly sessile at the ends of the stems. The calyx is somewhat hairy, with flat intercostal membranes (between the ridges). The flowers are tubular, with the 5 petal lobes angled perpendicularly away from the tube. The tube is about 9-17 mm long, with the lobes being 5 to 9 mm long. Flower color is white, pink, or a light blue.
Spreading phlox is a wildflower of middle to high elevations in the mountains. It is typically found in open forests or open rocky slopes.
Spreading phlox is found from the mountains of Vancouver Island, south through the Olympic Mts, and at Saddle Mt in the coast range of Oregon. It is widespread through the Cascades from southern British Columbia to the Sierra Nevada of California. Eastward, it ranges across northern Washington, Idaho, and Montana to the west slopes of the Rocky Mts. It may occasionally be found as far south as the mountains of central Idaho and northeastern Oregon.