Cyphobasidium usneicola (Diederich & Alstrup) Millanes, Diederich & Wedin

Basidiomycete fungus parasitic to Usnea.

      This species appears in the form off an almost spherical gall with a narrow base, 1-3 mm in diameter, typically muriform or cerebroid, pink, pale pinkish-brown, turning pale (or dark) when old, sometime colored by algae, Clamped hyphae. Basidia composed of two parts: an elongated thick-walled probasidia with an upper part (= meiosporangium) from which emerges at maturity an elongated thin-walled basidia carrying 4 orthogonal cylindrical epibasidia of 4-7 µm with a refractive end. Basidiospores elliptical with a refractive apex, 8.5-10 x 4-5 µm. Species described in Canada and North America, also found in Macaronesia, very rare in France and continental Europe (only one known station in Finistère) occurring on Usnea and in particular on Usnea articulata on which it develops particularly well and in a typical way.

N.B. Easily confused (and confused until recently) with  Biatoropsis usnearum of which  galls are not muriform and also differing in microscopic features.

Thanks to Paul Diederich who reported and determined this species and provided us with details on characteristics required for its identification.