Comfrey

Comfrey (Symphytum officinale) is a hardy perennial fast-growing herb. It is native of Europe and Asia and has been naturalized throughout North America. Comfrey has a black, turnip-like root and large, hairy broad leaves that bears small bell-shaped flowers which are mauve to violet in color to form in dense, hanging clusters. The plant blooms during the summer.

Toxic components
Comfrey contains eight pyrrolizidine alkaloids (PA), which are concentrated mainly in the roots (0.3-0.4%) but is also present in the leaves. The different types of PAs include: acetyllycopsamine, echimidine, heliosupine, intermedine, lasiocarpine, lycopsamine and symphytine. The PA content varies depending on the part of the plant, season, natural biological variation, and species. PAs are hepatoxins which can cause irreversible liver damage, through acute or cumulative consumption.