a genus of basidial fungi of the family Hydnaceae. There are approximately 500 species, which grow in forests on the ground, in rotting wood, and more rarely on living wood. Hydnum species with a cap have hymenophores shaped like conical thorns, papillae, and warts on their underside; species extending under the earth’s substratum have them on the upper side of the fruit body. Some Hydnum species that have a fleshy fruit body, such as wood hedgehog and variegated Hydnum, are edible when they are young.