Dichotomous table for gallers on Chaenomeles
by Hans Roskam
1a Malformations on leaves => 3
1b Malformations on stems => 2
2a Witches’ broom-like malformations with only little, often reddish leaves on sap-rich, whip-shaped shoots. C. speciosa: Inducer unknown, presumably caused by a fungus, Exoascaceae
2b Considerable cancer-like proliferations on basal stems. C. speciosa: Agrobacterium tumefaciens
3a Malformations on several terminal leaves caused by aphids => 4
3b Leaves with ± protruding bladder-like, pale-green or reddened swellings, later on withering, which at maturity are occupied by a grey-white layer of fungal asci. ? C. speciosa: Taphrina bullata
4a Leaves rolled inwards and crumpled, clustered nest-like on the ± shortened shoots => 5
4b Leaves obliquely bent downwards and ± rolled. C. japonica: Myzus persicae
5a Aphid with rather long siphunculi. Chaenomeles spp.: Aphis pomi
5b Aphid with short, thick, green siphunculi. C. japonica, speciosa: Rhopalosiphum oxyacanthae