narrowpetal wakerobin

Trillium angustipetalum is a rhizomatous perennial herb with one or more erect stems growing up to 70 centimetres (28 in) in height. There is a whorl of three large leaves generally described as bracts each measuring up to 25 centimetres (9.8 in) in length and round or somewhat oval. They are green and mottled with brownish or darker green spots. Each stem produces one flower, which is held on top of the bracts. The ill-scented flower has three lance-shaped green or red sepals and three narrow purple or maroon petals measuring up to 11 centimetres (4.3 in) long.

The plant is native to northern and central California and southwestern Oregon, where it occurs in forests, woodlands, chaparral, and riparian zones. It is found in the Klamath Mountains, western Sierra Nevada foothills, and Outer Southern California Coast Ranges.