Red Dock Spot

Ramularia rubella

"Ramularia rubella" is a plant pathogen in Ascomycota that infects "Rumex" species. Infection produces reddish spots on leaves. The red color is caused by the production of rubellin, a photodynamic anthraquinone-derived phytotoxin.
Ramularia rubella This is a picture of Ramularia rubella on a dock leaf at the Andover Equestrian Center in Linthicum, Maryland. Geotagged,Ramularia rubella,Spring,United States

Naming

"R. rubella" was originally described from "Rumex aquaticus" in Germany; it has a wide geographic range on "Rumex" species. It is being investigated as a biological control agent of "Rumex obtusifolius".

References:

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Taxonomy
KingdomFungi
DivisionAscomycota
ClassDothideomycetes
OrderCapnodiales
FamilyMycosphaerellaceae
GenusRamularia
SpeciesR. rubella