Butterbur, fuki in Japanese is a wild plant, native to Japan, China, Korea and Sakhalin and introduced to north America and Europe. The season is spring. Although originally a wild plant found in deep forest, most of the fuki found in supermarket are harvested at farms.
It has strong harshness or scum, therefore its roots and bulbs needs pre-treating, soaked in water for a certain period and boiled before cooking. The leaves are eaten as tempura and roots are preferred to be simmered.
Fuki tempura has bitter taste and this bitterness is the joy of this cuisine. Therefore fuki tempura comes with salt rather than tempura dipping sauce.