This first study is from 2012 and they explain how they made their extract from the entire plant. The second study is from 1862 where they explain how they essentially made a tea from the root of the plant. From these two studies, I believe you need to use at least the entire plant. Roots included especially because according to the older study, the Micmac Indians said the compound is found in the roots of the plant. In the 2012 study they used the entire plant.
This first study is from 2012 and they explain how they made their extract from the entire plant. The second study is from 1862 where they explain how they essentially made a tea from the root of the plant. From these two studies, I believe you need to use at least the entire plant. Roots included especially because according to the older study, the Micmac Indians said the compound is found in the roots of the plant. In the 2012 study they used the entire plant.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3302891/
https://ia800708.us.archive.org/view_archive.php?archive=/22/items/crossref-pre-1909-scholarly-works/10.1016%252Fs0140-6736%252802%252960584-7.zip&file=10.1016%252Fs0140-6736%252802%252960988-2.pdf