Causing protruding tongue-like enlargements of bracts and ovaries of female catkins of Alnus incana [rugosa] and A. rugosa [serrulata]. The tongues appear on the catkins near pollination time and are then very small: 2-3 mm. long. Later in the season when the fruits of the alder are well grown the tongues may measure several millimeters in length. Occasionally also causing leaf curl (involving all or part of the leaf), with typical thickening of leaves, on the same hosts.

[Mix 1954 pg. 58 updates the host names to A. rugosa and A. serrulata based on a revision of Alnus that had been published in the intervening years.]