A new species of Albugo on Pterostylis (Orchidaceae) from Australia: confirmation of the genus Albugo on a monocotyledonous host.

Albugo macalpineana sp. nov., causing white blister disease of terrestrial orchids in the genus Pterostylis, is described from Victorian and South Australian specimens more than 50 years old. Subglobose sporangia have uniformly thickened walls, and oospore walls show a raised cerebriform ridge pattern. This rare fungus has not been collected since 1954. The work reported confirms earlier entries in South Australian and Victorian plant disease lists of the occurrence of the genus Albugo on a monocotyledonous host.