Herbs or shrubs, mostly natives of western North America; often hairy; with no stipules; the leaves mainly alternate or from the root; the flowers chiefly blue or white, often in coiled clusters; the calyx with five united sepals; the corolla with five united petals; the stamens five, on the base of the corolla and alternate with its lobes, with threadlike filaments and usually with swinging anthers; the ovary superior, the styles two or two-cleft; the fruit a capsule, containing few or many seeds. The leaves were formerly supposed to have water-cavities in them, hence the misleading name. Some of this family resemble some of the Borages, but the stamens are long, the styles are two, at least above, and the ovary has not the four conspicuous lobes of the latter family.

There are many kinds of Phacelia, hairy plants, with no appendages between the sepals; resembling Hydrophyllum, except that the petals overlap in the bud, instead of being rolled up, and the seeds are different. The name is from the Greek, meaning "cluster."