E-Flora BC: Electronic Atlas of the Flora of British Columbia

Summary:
Savile (1959) differentiated this species primarily microscopically from Exobasidium vaccinii and Exobasidium vaccinii-uliginosi. Spore size, basidium size, and the number of sterigmata per basidium are more or less intermediate between those two species as Savile described them. Spore shape is clavate (nearly cylindric in E. vaccinii, broadly clavate to elliptic in E. vaccinii-uliginosi). "The habit, the frequently septate spores, and the production of conidia separate it sharply from [E. vaccinii-uliginosi]." A variety minor is also described which differs in spores and basidia. "This variety approaches E. vaccinii in spore size, but the clavate spores and the preponderance of basidia with three sterigmata indicate its affinity with E. cordilleranum" (Savile, Latin names italicized).

Collections were examined from BC (both varieties) and from the Idaho-Montana border (var. minor), (Savile).

Fruiting body:
forming pale spots [maculas pallidas] about 0.4-0.8cm across on leaves without hypertrophy

Microscopic:
spores 14.0-19.0 x 3.5-6.3(7.0) microns, clavate, 0-1(3) septate, hilum hooked; basidia 2-3(4)-spored, extending (14)19-31 microns beyond the cuticle, 3.5-7.5 microns wide, sterigmata 4.5-6.0 x 1.3-1.8 microns; conidia 3.5-10.0(14.0) x 0.8-2.0 microns, acicular, (Savile), spores (11.0)13.0-16.5 x 3.0-4.5 microns, 0-1-septate; basidia 4.0-6.3 microns wide, extending about 20 microns beyond the cuticle, (Savile for var. minor)