DESCRIPTION: A mite-induced gall that is seen in numerous clusters over the upperside of the leaf. Each gall starts off yellowish before becoming greener and then taking on a reddish to brown coloration.  Each gall measures up to 3mm in diameter and there is a small opening on the underside. The mites leave the gall in autumn and spend the winter in empty alder cones or bark crevices.  DISTRIBUTION: Widespread. Best seen from May to October. HABITAT: On the leaves of Alder.