Petasites -species contain livertoxic pyrrolizidine alkaloids. Read more here. -Henriette
A VERY singular and very conspicuous plant, not unfrequent with us in wet places. The flowers appear before the leaves, and they would hardly be supposed to belong to the same plant. The stalks are round, thick, spungy, and of a whitish colour, and have a few films by way of leaves upon them. On the top of each stands a spike of flowers, of a pale reddish colour; the whole does not rise to more than eight inches in height. These appear in March. When they are dead, the leaves grow up; these are roundish, green on the upper side, and whitish underneath, of a vast bigness, and stand singly upon hollowed foot-stalks, of a purplish, whitish, or greenish colour; they are often two feet broad. The root is white and long, it creeps under the surface of the ground.
The root is the part used; it is praised very highly, as a remedy in pestilential fevers; but, whether it deserves that praise or not, it is a good diuretic, and excellent in the gravel.