Aceria fraxinivorus, the cauliflower gall mite,[5] causes the ash key gall that is found on the inflorecences commonly called the flowers or seeds.[6] The hanging seeds are the "keys" of the common ash tree (Fraxinus excelsior).

Appearance and causeEdit

The gall presents usually as a sizable irregular deformity formed from fused and swollen flower stalks (pedicels),[8] however it has also been found on buds, leaf stalks, twigs or trunks.[9] It is brown when fully formed, finally black, but green at first.[1] Once the leaves have fallen, the galls, filled with mites, are very obvious within the trees branches and may remain for a year or more.[5] Leaflets or entire leaves and petioles may also be involved, with additional distortions such as thickening and leaf lamina rolling, especially when the tree is heavily infested.[8]

The cause of the gall are mites, mainly female, the eggs being viable without fertilization. These gall-mites are specialist species; they are cylindrical and feed on sap, and have no circulation or respiratory systems, only two pairs of legs and no eyes.


The ash key gall is widespread in Britain; its numbers vary with the changes in annual seed production levels.[1] In France and the Netherlands they are known as cauliflower galls.