This species causes a well-known and much studied disease on the horticultural "azaleas." Numerous (all?) cultivars are more or less susceptible ...

Entire leaves or parts deformed into very conspicuous, pale, fleshy, shapeless galls up to 3 cm across, eventually hymenium-clad and chalky white on the morphological underside.

Exobasidium japonicum (Exobasidiales, Basidiomycota) is a fungus that causes the development of galls in tender tissues of azalea (Rhododendron spp.) ... Depending on the organ that develops from the infected apical, axillary or adventitious buds, the galls are formed by tissue of leaf, stem, or flower organs.