The brown roll-rim fungus, (Paxillus involutus) is a highly toxic mushroom found on the Barff around the birch woodlands and is known for its dangerous effects on human health.

It has a distinctive brown, velvety cap that is flat or funnel-shaped, with edges that roll under to protect the gills. The cap can be brownish-yellow and becomes smooth and shiny as it ages. The gills are pale brownish-yellow and bruise wine-red when damaged. The stem is short, cream-colored, and darkens below.

This fungus typically grows in broadleaved woodlands, particularly those with birch trees, and can also be found in parks and gardens. It is common throughout the UK.

The brown roll-rim is known to be deadly poisonous. It contains toxins that can cause severe autoimmune reactions, leading to hemolytic anemia, kidney failure, and potentially death. Symptoms may not appear until days or weeks after consumption, making it particularly insidious.