Exobasidium parvifolii

Exobasidium darwinii

Exobasidium parvifolii Hotson on Vaccinium parvifolium Sm. and V. ovalifolium Sm. in North America forms perennial galls on the stems from which numerous cylindrical, clavarioid excrescences emerge. Nannfeldt (1981) interpreted these structures as highly disorganized shoots, which, however, cannot be [considered distinct] witches’ brooms ...

Fungus produces conspicuous witches’ brooms on the host plant [a Hawaiian endemic] through continuing proliferation of small young branches; infected twigs often somewhat deformed, contorted and accompanied with swellings. Infected leaves uniformly bright red on both sides, not hypertrophied and not enlarged in comparison with healthy leaves; hymenium hypophyllous, quite delicate, composed of basidia, basidiospores and conidia. Basidia emerging singly or in fascicles through stomata or directly from disintegrated epidermis, hyaline, cylindrical, 20–30 μm long, 3.9–5.6 μm wide, apically rounded and ended with 3–4 sterigmata.

Exobasidium darwinii, a new Hawaiian species infecting endemic Vaccinium reticulatum in Haleakala National Park