Melanustilospora ari (Cooke) Denchev, 2003
on Arum, Biarum
parasite
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.
host plants
Araceae, oligophagous
Arum besserianum, cylindraceum, elongatum, italicum, maculatum, orientale subsp. danicum; Biarum tenuifolium.
synonyms
Melanotaenium ari.
notes
The description above is based on photos in the website of Julia Kruse (Pflanzenbestimmung) and Vákny (2012a). 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

underside
references
Almaraz (1998a), Buhr (1964b), Denchev (2003a), Klenke & Scholler (2015a), Kruse (2019a), Lotze-Engelhard (2010a), Mayor (1975a), Redfern & Shirley (2011a), Savchenko, Dzyunenko & Heluta (2010a), Savchenko & Heluta (2012a), Scholz & Scholz (2013a), Tomasi (2014a), Tóth (1994a), Vánky (1994a, 2012a), Vánky, Lutz & Bauer (2008b).