Anamorph: colonies on either side of leaves, effuse or forming white patches, sometimes evanescent. Appressoria variably shaped, papillate or lobed, sometimes inconspicuous. Conidiophores erect, the basal cell (20-) 30-50 x (6-) 7.5-10 µm. Conidia formed in chains, usually with two or three immature conidia at the base of the chain. Conidia (20-) 25-35 (-38) x (12-) 13-18 (-22) µm, cylindric-ellipsoidal, ± octagonal in transverse section, thin-walled, hyaline, aseptate, the surface smooth or with inconspicuous striate to dendritic ornamentation, containing fibrosin bodies, without a gelatinous sheath or appendages. Microconidia also frequently produced from smaller conidiophores, the conidia measuring 12-18 x 5-12 µm.
Teleomorph: ascomata cleistothecia, scattered or in small clusters, 150-180 (-200) µm diam., globose to slightly oblate, black in surface view when mature. Peridium dark brown, composed of thick-walled angular cells 8-12 µm diam., the upper part covered with complex hyaline smooth thick-walled refractive appendages. Appendages to ca 100 µm in length, when mature usually with 2-3 bifurcations or rarely trifurcations in the top third, the apices circinate or slightly helically coiled. Interascal tissue not seen. Asci 6-12 per ascoma, 50-85 x 30-55 µm, ± globose to obpyriform with a papillate apex, almost sessile, thick-walled but not fissitunicate, fracturing irregularly, 8-spored. Ascospores 23-27 x 12.5-14 µm, cylindric-ellipsoidal to ovoid-cylindrical, sometimes weakly fabiform, hyaline, aseptate, thin-walled, without a gelatinous sheath or appendages.
Not formally assessed, but the species is widespread and would certainly be considered as of Least Concern.
Sawadaea tulasnei is similar but has smaller macroconidia and ascomatal appendages that are mostly simple or bifurcate. It is found as an associate of Acer platanoides, not A. pseudoplatanus or A. campestre.
In GB&I, restricted to living leaves of Acer pseudoplatanus and A. campestre. It has very occasionally been reported elsewhere on Aesculus hippocastanum, but this appears to be a temporary association.
Reported from all regions of GB&I, and probably coextensive with its host plants.
The species is a parasite, but does not appear to cause significant damage to its host. Affected leaves may show extensive colony development, especially in shady conditions.