Cystotheca castanopsidis

Many Cystotheca species form dense, white or brown, distorting patches on the leaves of their hosts. Some species in this genus are also known to cause witch's-broom galls. Cystotheca castanopsidis, like most Erysiphaceae, is highly host-specific and only infects species in the genus Castanopsis.^[1] Also found on the same genus are Cystotheca tjibodensis and Cystotheca esetacea. C. esetacea is characterized by forming brown mycelium without aerial hyphae.^[2]

The fungus was formally described in 2012 by Jamjan Meeboon and Susumu Takamatsu with the basionym Setoidium castanopsidis,^[1] before being transferred to the genus Cystotheca in 2017.^[3] The species epithet refers to the host genus. The type specimen was collected in Indonesia.