Haasiella is a fungal genus in the family Hygrophoraceae. It is a monotypic genus that contains only the species Haasiella venustissima. Haasiella splendidissima, formerly considered to be a distinct species based on its 4-spored basidia, was found by a DNA study to be synonymous with Haasiella venustissima. Haasiella venustissima is only known from Europe and is saprotrophic on wood. Haasiella was described as a new genus in 1966 by Czech mycologists Frantià ¡ek Kotlaba and ZdenÃÂk Pouzar. It is most closely related to the genus Hygrophorus.
The genus name is in honour of Hans Haas, a German mycologist, who was a specialist on Agaricus from Schnait near Stuttgart.