This photo shows a close-up of the flat-topped inflorescence of yarrow as seen in "sandy" volcanic soils along the Timberline Trail above the Cloud Cap Chalet in the Mt. Hood Wilderness...........August 2, 2007. Individual flower heads can be seen here, each with up to a dozen central, disk flowers surrounded by 3-6 ray flowers.
Yarrow is perhaps the most numerous plant in the inland Pacific Northwest. It is a native, but can sometimes be very weed-like It is an upright perennial with one main stem and occasional branching. The stems arise 3-30 cm tall. The herbage is smooth to pubescent. The basal and stem leaves are pinnately dissected, with only the lower ones petioled. The leaves alternate along the stem and are up to 15 cm long.
The inflorescence is a flat-topped corymb consisting of numerous small flower heads consisting of 3-5 white rays surrounding a tiny disk of 10-30 white flowers. The rays are 2-3 mm long.
Yarrow is found in multiple habitats, from alpine to forest, to roadside and plains.
Yarrow is found over much of the northern hemisphere. On the east coast of North America, it is most likely an import from Europe.
This photo shows a close-up of a pinately compound basal leaf of yarrow as seen in "sandy" volcanic soils along the Timberline Trail above the Cloud Cap Chalet in the Mt. Hood Wilderness...........August 2, 2007. The leaf consists of numerous (not a thousand however) segments that are further divided.
-Yarrow as seen above timberline along the Butte Camp Trail, Mount Saint Helens........July 9, 2013.
Yarrow as seen on the Pumice Plain at Mt. St. Helens National Monument.........July 26, 2015.
-Yarrow as seen near the summit of Lookout Mountain, Badger Creek Wilderness........July 17, 2016.
Yarrow blooming along the Loowit Trail in a moist area at the southern base of Pumice Butte, eastern edge of the Plains of Abraham, Mount St. Helens National Monument...........July 13, 2016.