Lactarius acerrimus is a member of the large milk-cap genus Lactarius in the order Russulales. It was first described by Max Britzelmayr in 1893.[1]
The mushroom's cap has between 5 and 15 cm in diameter. It sometimes takes a funneled shape when old. The lamella is cream-coloured when young, taking on an ochre colour as it matures. Its edge is smooth, undulated and irregular. The stem is short and stubby, measuring between 2 and 5 cm in length, and between 0.8 and 2 cm thick.
The species can be found mainly in Europe, but has been reported in North America and in Morocco.