This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Pretty annual herbs of dwarf habit, remarkable for the slender calyx-tube, which is elongated far above the seed-vessel. Calyx-limb deciduous. Petals 4, clawed, 3-lobed or obcordate. Stamens 4. Capsule 4-celled, dehiscing through the cells; seeds numerous. There are only two species, both natives of California. Name from Evxapis, agreeable.
E. grancliflorum of gardens appears to be merely a large-flowered variety of the foregoing.