Acalitus brevitarsus

Erineum alneum
Phytoptus purpureum
Phyllerium alnigenum
Phytoptus brevitarsus

Hosts: Alnus glutinosa, cordata, hirsuta, incana, incana ssp. rugosa, pubescens, rugosa, viridis

Relationship: Erineum patches, white to yellow and orange, on leaf undersides

Range: WV, Europe

Host associations with other non-Alnus plants are probably missidentifications, such as Betula, Juglans, etc. Erineum on alder in the USA may be caused by a different species from Acalitus brevitarsus in Europe.