The Latin specific epithet rivale means "growing by streams", a reference to a preferred habitat.

[6] Pseudotrillium rivale is a perennial, herbaceous, flowering plant that persists by means of an underground rhizome.

It differs from Trillium in that it has spotted petals, leathery leaves with a cordate base, and a continuously elongating pedicel.

[9] Its type specimen was collected in 1880 at Big Flat in the Siskiyou Mountains, thirty miles east of Crescent City, California.

Based on morphology and molecular phylogenetic evidence, Trillium rivale was segregated into a monotypic genus by Susan B.

[11] Based on molecular phylogenetic studies, Pseudotrillium rivale is the first diverging (basal) branch of Parideae, a result that is well supported.

[7][15] Under its former name, Trillium rivale, this plant has gained the Royal Horticultural Society's Award of Garden Merit.