Cortinarius elaiochrous is a mycorrhizal fungus that grows only with beech trees. A mushroom that cannot live without its partner. The cap is three to eight centimetres across, brownish to violet, often with a sticky surface when wet. The gills are violet when young, turning rusty brown as the spores mature. The stalk is four to ten centimetres tall, often with a bulbous base. A mushroom that changes colour as it ages. The name Cortinarius comes from the cortina, a web-like partial veil that covers the gills in young specimens. This veil is made of fine, silky fibres, like a cobweb stretched across the underside of the cap. As the mushroom matures, the cortina breaks, leaving a ring zone on the stalk and often traces of the web on the cap margin. A mushroom that wears a cobweb when young. The spores are rusty brown, a distinctive feature of the genus. When a Cortinarius cap is placed on a piece of white paper overnight, a rusty-brown spore print appears in the morning. This colour helps distinguish Cortinarius from other purple or brown mushrooms. Cortinarius is one of the largest genera of fungi, with thousands of species worldwide. In New Zealand, many species are endemic, found nowhere else. They are an important part of the beech forest ecosystem, forming partnerships with the trees that dominate native forests. This species is endemic to New Zealand. It is found in beech forests in both the North and South Islands, appearing in autumn after rain. Not edible. Some Cortinarius species are poisonous, and this one is too rare to risk. The beech forest is damp. The Cortinarius grows, violet gills fading to rust, cobweb veil breaking. It does not know it is rare. It does not know it is poisonous. It just wants to trade nutrients with a tree. That is what mycorrhizal fungi do.