Summary: Coccomyces arbutifolius is included as an example of the ascomycete order Rhytismatales. It produces tiny, densely gregarious fruitbodies on leaves of Arbutus menziesii. They develop subdermally and open irregularly by teeth or a slit, on discolored spots. Unlike Coccomyces dentatus, the discolored spots they grow on are not bleached or bounded by a dark line, but they are marked by a faint whitish bloom.
It was described from Vancouver BC.
Fruiting body: fruitbodies subepidermal, 0.02-0.1cm across, dark brown, "irregular and often somewhat elongate in outline, without a preformed dehiscence mechanism, opening irregularly by teeth (sometimes by a longitudinal slit)" "on discolored spots not bleached or bounded by a line stroma, but marked by a faint, whitish, superficial bloom"
Microscopic: spores 75-100 x 2.5 microns, nonseptate, prominently sheathed; asci 8-spored, 120-150 x 15-20 microns, clavate, long-stalked; paraphyses filiform, simple or occasionally once-branched, enlarged to 2.5 microns at the apex; pycnidia scattered among the apothecia, subepidermal, hypophyllous, "flattened, irregular in outline, dark brown, consisting of a covering layer of dark brown isodiametric cells" 2.5 microns in diameter "and a basal palisade of colorless, simple conidiophores" 15 x 1.5 microns, "with a narrow neck and no collarette"; conidia "simple, colorless, bacilliform", 3.5-5 x 1.0 microns
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