Today's images are the results of my very first attempts using a new piece of software to process the raw files. I also used a point-and-shoot camera instead of my usual SLR.
Pseudotrillium rivale is a relatively recent moniker for this species. Formerly named Trillium rivale (and still known horticulturally as such), it is a Siskiyou Mountains endemic tolerant of ultramafic soils. Its separation from the genus Trillium is due in part to the molecular phylogenetic work of Susan Farmer; see: S. Farmer and E.E. Schilling. 2002. Phylogenetic analyses of Trilliaceae based on morphological and molecular data. Systematic Botany 27(4):674-692. For some of the morphological differences, read Recent and Continuing Studies in Trilliaceae (reprinted from BEN #301): spotted petals, an elongating pedicel, and (in many individuals), glossy, heart-shaped, Philodendron-like leaves. On our trip to the Siskiyous, we saw enormous variability in this latter characteristic, and the particular individual plant in today's photograph was the foremost exception. Also exceptional was the fact that I don't think we spotted any plants growing near a watercourse, despite its common name of brook wakerobin.
Calphotos has a good set of photographs: Pseudotrillium rivale. You can also have a look at this image of a garden-grown plant by Silver Creek Garden @ Flickr. Lastly, if you are a Trillium enthusiast, then Trillium-L is the discussion list for you!
Botany resource link: Cactus adaptations to dry environments from the Mauseth lab at the University of Texas at Austin. Follow the menu items along the left side of the page; the botanical information is fascinating (and illustrated!), while the travel section is both funny and (occasionally) discomforting.