Nabalus albus (also known as Prenanthes alba)

White Rattlesnakeroot 

Also known as White Lettuce and Lion's Foot

• Partial to deep shade
• Average to moderately wet or dry soils
• Up to 48” tall
• Late summer and fall blooming
• Native to Ontario, happy in Woodland and Forest settings.

New to my garden this year but, after ordering these seeds from Prairie Moon, I found out that they are not new to the woods at our Perth place, where I came across a blooming patch last September. In that very dry, shaded setting they grew to between 2' and 3'-6". In a higher moisture setting, with a bit more sunlight, they can grow to around 4' tall and have a width of around 18". Further digging through old photos unearthed a picture of their spring foliage, which is distinctive enough that it caught my eye long before I knew what species I was photographing. 

With a relativly quick lifecycle, these grow either as re-seeding biennials or short lived perennials. 

First photo by peganum via Wikimedia Commons