The Aphrophora genus can be recognised by their large size in comparison to other froghopper species, and the pale ridge (‘keel’) running down the midline of the head and pronotum. The four species that occur in Britain can be distinguished by their markings. 
 
The background colour of A. alni is pale to mid-brown with two distinct white patches along the margin of the wings. It can be confused with similarly-coloured variants of Philaenus spumarius, but P. spumarius is noticeably smaller and does not have the raised keel on the head. The upper surfaces of Aphrophora species are covered with tiny black pits and are shiny, contrasting with the matt surface found in Philaenus produced by a covering of minute fine white hairs.