Hydnellum caeruleum

Hydnellum caeruleum, commonly known as the blue-gray hydnellum, blue-green hydnellum, blue spine, blue tooth, or bluish tooth, is an inedible fungus found in North America, Europe, and temperate areas of Asia.

The young caps have shades of blue, gray and brown, with light blue near the margin. The stem is orange to brown. The flesh is blue to black in the cap, and red to brownish in the stem. The blue hues tend to fade with age.

H. aurantiacum is very similar to mature specimens but differs in color. H. suaveolens is similar, with mostly blue flesh and odour of anise.