***Psuedotrillium rivale This is a very technical article detailing the authors research and reasons for the renaming of Trillium rivale.  http://www.goldsword.com/sfarmer/Article/
Psuedotrillium rivale is the new name being given to Trillium rivale.  The research done to arrive at the decision for a new name was done by Susan Farmer.  The link to the right is to the research paper done by Susan.  Following is a description of the work and reasons for the new name.  
On a molecular level, Trillium rivale was so distinct from both Paris s.l. and Trillium, that everything either had to become all one genus -- or we had to do some splitting. I tend to be a splitter -- I like nice discrete boxes, not a single box with a lot of "exceptions".

Morphologically, you've got the spotted petals which are unique in the family, the pollen is trillium-like, but the cotyledon is paris-like. There's those heart-shaped philodendron-like leaves. The folks on the TRILLIUM-L list claim that it's never in the 3-leaved state without a flower unless it's been damaged by herbivory. Then there's that elongating pedicel; nivale does that too, but I don't think it elongates to the point of pressing the fruit into the soil.

Susan Farmer 2/7/03