Burdock root
The long, slender root of the greater burdock plant, brown outside and pale inside, with an earthy, faintly sweet flavour and a firm, fibrous texture.
Gobō is the root of the greater burdock, grown as a vegetable in Japan, where it can reach up to a metre in length. It tastes earthy, nutty and slightly sweet, and it stays firm and fibrous even after long cooking, which makes it suited to braises, soups and quick stir-fries of thinly cut strips. Much of the flavour sits just beneath the skin, so it is scraped with the back of a knife or scrubbed rather than peeled. Cut surfaces brown quickly, so the pieces are usually dropped into cold water or lightly acidulated water, which also softens its astringent edge. Fresh roots are found in Asian grocers, especially Japanese and Korean shops, and occasionally at farmers' markets or organic farms; frozen, pre-cooked or pickled versions are also available by mail order.
Substitute:
The closest match is salsify, which has a similar earthy taste, browns just as quickly and has a comparable shape, but is softer and milder and cooks faster. Parsnip or parsley root capture the sweetness but not the fibrous bite or the astringent, woodsy flavour, so the dish turns out softer and sweeter.