Cortinarius rotundisporus, also known as the elegant blue webcap, is a basidiomycete mushroom of the genus Cortinarius found in southern Australia, where it is found in eucalypt forests and rainforests. The cap of the fruiting body is a steely blue colour, with a yellowish boss, and paler similarly coloured stipe.
The cap ranges from 2.5 to 7 cm (1–3 in) in diameter, and is initially convex before flattening. It has a slight boss which is mustard-, honey- or cream-yellow tinged and steely blue elsewhere. The adnate gills are creamy or lilac-tinged early, and darken with the spores. The slender 5-7.5 cm (2–3 in) stipe lacks a ring; it is pale yellow or white with a tinge of the cap colour. The flesh is yellowish and may have a lilac or pale blue tinge. The spore print is reddish brown and the oval to round spores measure 8.5 × 6.5 µm. There is no particular taste or smell. Potassium hydroxide will produce a pink-purple reaction in the stipe or cap. The mycelium is white.
It can vary in colour, from dark blue-black to a pale yellow-brown as it dries.