This is a beautiful marginal roll gall of bracken. When seen under a microscope, it looks like a delicate, pale, lime-green lace border on the underside of the pinnule. The first indication of infestation is a characteristic discoloration and distortion of the pinna. The affected pinna is generally yellowish, later turning brown. The galled pinnules are abnormally small and distorted, with a thickening of reflexed margins. The indusium, which becomes enlarged, contains mites and lime-green erineum like hairs. The infestation occurs in June-July.

- Hartford Keifer,Edward Baker,Tokuwo Kono,Mercedes Delfinado,William Styer: (1982) An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America^©