Melanustilospora ari (Cooke) Denchev, 2003
Relatively extensive, ill-delimited, greyish green leaf spots, not delimited by veins. The infection is inconspicuous, the leaf surface is only lightly swollen. Embedded in the leaf tissue lie masses of roundish, yellow-brown spores with a smooth, double wall of uneven thickness, 13-17 µm in diameter.
The description above is based on photos in the website of Julia Kruse (Pflanzenbestimmung). Carina Van Steenwinkel has studied plants with blackish swollen spots like in the pictures below, and found that these spots have nothing to do with the fungus and probably are not pathological at all.
Arum maculatum, Belgium, prov. Namur, Lavaux-Sainte-Anne © Chris Snyers
Almaraz (1998a), Buhr (1964b), Denchev (2003a), Klenke & Scholler (2015a), Lotze-Engelhard (2010a), Mayor (1975a), Redfern & Shirley (2011a), Savchenko, Dzyunenko & Heluta (2010a), Savchenko & Heluta (2012a), Scholz & Scholz (2013a), Tomasi (2014a), Tóth (1994a), Vánky (1994a), Vánky, Lutz & Bauer (2008b).