Hydrophyllum occidentale is a species of flowering plant in the waterleaf family known by the common name western waterleaf. It is native to the western United States from California to Idaho, where it grows in a variety of habitats from wet mountain meadows to dry chaparral slopes. This is a rhizomatous perennial herb producing a patch of leaves, most of which are made up of many pairs of oval-shaped, bluntly lobed green leaflets. These compound leaves may be up to 40 centimeters long. The plant produces erect stems branching into green to reddish-purple rough-haired, leafless peduncles bearing flower clusters. The flower cluster is a large ball of densely packed flowers. Each flower is up to a centimeter wide and bright white to lavender. It is coated in downy white hairs and has a long protruding style and usually five stamens with large purple or red anthers. The fruit is a spherical capsule containing two seeds.