Dichotomous table for gallers on Calluna vulgaris
by Hans Roskam
1a Malformations ± witches’ broom-like => 2
1b Leaves clustered at shoot tip, imbricated covered, transformed into a bud-like, egg-shaped gall. Inducer unknown
2a Shoots may bear witches’ broom-like malformations. Many very small (0.1‒0.2 mm) orange uredinia on underside of leaves, which soon fall. Thekopsora fischeri
2b Thin twigs abnormal, twig slightly inflated at insertion. Mytilaspis pomorum
2c Plant with small witches’ broom-like malformations of shoot; leaves clustered, reduced, often ± abnormally pubescent, usually pale-green or reddish discoloured. Aceria exigua
= The rust fungus Thekopsora ericae causes witches’ brooms. Uredinia on underside of leaf, 0.1‒0.2 mm across