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Species Information
Summary: Ciborinia whetzelii produces brown cup-shaped stemmed fruitbodies arising in the spring from overwintering black sclerotia that develop on browned aspen leaves giving an "inkspot" appearance and later fall to the duff leaving "shotholes" in the leaves. It is common throughout BC (Allen).
It is found in BC (Allen), and throughout Canada and the northern United States, but the sexual state has not yet been documented in BC, (Callan). It occurs specifically in PQ and NY, (Seaver).
Upper surface: 0.2-1cm, at first cup-shaped, expanding and becoming subdiscoid [nearly disc-shaped]; brownish; sclerotia form on living leaves, circular or irregularly subcircular in form, persistent or dehiscent, (Seaver), sclerotia form dark "inkspots" on living leaves that drop out in late summer leaving shotholes, (Allen), browning of foliage is followed in about one month by circular to elliptic black sclerotia on infected leaf blades; sclerotia are 0.2-0.8cm across, black, circular to oval or with rounded irregular outlines; sclerotia begin to fall from infected leaves as early as mid-July, and leaves may remain attached to the tree, bearing characteristic "shot-holes"; overwintered sclerotia germinate on the surface of deep moist duff under aspen and give rise to fruitbodies by the hundreds; fruitbodies are 0.2-1cm across, cup-shaped, pale brown, (Callan)
Underside: brownish (Seaver)
Stem: 0.5-2.5cm long (Seaver, Callan)
Microscopic: spores 11-16 x 4-7 microns, elliptic, uniseriate; asci reaching a length or 150-200 microns and width of 9-12 microns, (Seaver), spores 7-10 x 3-4 microns, oval, single-celled, colorless; asci 8-spored, 160-180 x 11-12 microns, club-shaped, with a small apical plug that stains blue in Melzer''s reagent; sclerotia have a distinctive palisade layer of cells just under the outer surface, (Callan), paraphyses numerous (Funk)
Habitat / Range
fruitbodies on sclerotia lying on ground that have dehisced from the leaves of Populus tremuloides, (Seaver), sclerotia on aspen and cottonwood leaves, (Allen), on aspen, rarely on balsam poplar, (Callan)
Similar Species
Ciborinia seaveri Groves and Bowerman, common in Alberta and eastern Canada but not reported in BC, produces similar symptoms in leaves, but the sclerotia are smaller, averaging 0.3-0.5cm across, and occur mainly on veins and petioles rather than leaf blades, (Callan).
