Beefsteak fungus (Fistulina hepatica) is a soft, tongue-shaped bracket fungus that grows low on the trunks and stumps of oak and sweet chestnut, so uncannily like a slab of raw meat that it bleeds a red juice when cut and shows a marbled, flesh-pink interior. Sharply acidic and a little chewy, its liver-red flesh has long been sliced thin to eat raw in salads or braised slowly as a tart, meaty substitute for beef.