Problems with Caltha species

[Gerdk]

After a normal and healthy growth in spring and early summer the leaves of my Caltha species (C. palustris alba, C. polypetala, C. sagittata) started to show the symptoms as demonstrated by the attached pictures.
I suspect this is a physological disorder caused by the sun but I am not sure.
Are there some other growers which have the same problem?
Unfortunately (in this case) my small garden is surrounded by a wall, so there is not much air circulation during hot spells.

Gerd Knoche, Solingen
Germany

[Susan Band]

Have you been having it really hot? If so I would check for red spider. Otherwise it is probabally what you said just sunburn.

[Gerdk]

Susan,
Thank you. This morning I checked for spider mites. There are no signs of an infestation. So I agree, the damage most probably was caused by the sun.
Gerd Knoche, Solingen
Germany