Hi Julie,
I do not think that they have updated this. I have been doing my own research on Trillium since meeting Fred Chase. There is a woman doing genetic research on the genus. I have only seen one true T. parciflorum and lots of T. albidum, which some books call T. chloropetalum. T. parviflorum has very, very, very tiny petals, between 1/4 to 1/3 of an inch. T. albidum has petals to 21/2 - 31/2 inches.

Hope this helps,
Jason

There are multiple trilliums with sessile flowers, the 1997 F. W. Case/R.B. Case trillium book gives full entries to both T. chloropetalum and T. parviflorum, with the latter being a recently recognized species resembling T. albidum. No mention of T. parviflorum is made under T. chloropetalum, which is definitely not given as a synonym of T. parviflorum.

Did somebody shuffle things up since then, using DNA studies?

Let me try to clarify a bit. There are three Western sessile Trillium which are or can be white. Trillium chloropetalum, T. albidum and T. parviflorum.

According to "Trilliums" by Frederick W. Case Jr. and Roberta B. Case, the range of Trillium chloropetalum (sessile and can be white) is the central California coast region. Fruit purple. Flower petals 35-65mm = 1.38"-2.6".

The USDA plants website has the range for chloropetalum into northern California but not into Oregon.

Albidum - sessile and most often white - range (Case)central California north to central Oregon. USDA - Central California up through Oregon and into Clark County Washington. Case notes that where cloropetalum and albidum overlap there has been hybridizing. Fruit of albidum is green or purplish-green (Case). Flower petals 48-78mm = 1.88"-3.07" quite large.

Parviflorum (Victor G. Soukup)- sessile creamy white, occassionally purple stained range NW Oregon north into Pierce & Thurston counties in Washington. USDA has the range only in Washington. Fruit is dark-red purple or maroon. Flower petals are 30-40mm = 1.18"-1.57" (considerably smaller than albidum but not 1/4-1/3 of an inch)

Plants of the Pacific Northwest Coast incorrectly lists the Washington sessile Trillium as chloropetalum. I was told they should fix it in the new revision. Guess I'll have to track down a copy and check.

Susan Farmer has been doing DNA research on Trilliaceae. She has a wealth of information on her website.

Thank you.
Julie

Here is a link that might be useful: Susan Farmer Trillium site