The hydnoid fungi are a group of fungi in the Basidiomycota with basidiocarps producing spores on pendant, tooth-like or spine-like projections. They are colloquially called tooth fungi. Originally such fungi were referred to the genus Hydnum, but it is now known that not all hydnoid species are closely related.

Hydnum repandum, commonly known as the sweet tooth, pig's trotter, wood hedgehog or hedgehog mushroom, is a basidiomycete fungus of the family Hydnaceae. First described by Carl Linnaeus in 1753, it is the type species of the genus Hydnum. The fungus produces fruit bodies (mushrooms) that are characterized by their spore-bearing structures—in the form of spines rather than gills—which hang down from the underside of the cap. The cap is dry, colored yellow to light orange to brown, and often develops an irregular shape, especially when it has grown closely crowded with adjacent fruit bodies. The mushroom tissue is white with a pleasant odor and a spicy or bitter taste. All parts of the mushroom stain orange with age or when bruised.