Bracken fern (Pteridium aquilinum) is a fern plant that is cultivated in east Asia, especially Japan, its starchy rhizome that is ground to make warabiko flour.
The young shoots and leaves of bracken fern are said to taste of asparagus, almond, and kale. Unfortunately they also contain high levels of the carcinogenic compound ptaquiloside. Ptaquiloside is nearly entirely destroyed by boiling, but a number of health agencies advise against eating bracken fern at all.
Farming of the bracken fern is very difficult, since the rhizome matures over several years, and the yield of warabiko from a mature rhizome is only 1-2%, by weight. The production of true warabiko is now quite limited and artisinal.