Dichotomous table for gallers on Erucastrum
by Hans Roskam
1a On parts above ground => 3
1b On roots or root collar => 2
2a Succulent, broad spindle-shaped or acuminate cylindrical, compact swellings on main- and major side roots. E. gallicum, nasturtiifolium: Plasmodiophora brassicae
2b Almost globular, 5‒10 mm long, one- also several-chambered swellings close to root collar. Containing a single white larva. E. gallicum: Ceutorhynchus assimilis
3a On leaves and stems => 4
3b Flowers swollen; unopened. Calyx enlarged, corolla and anthers necrotic. Stamens and stigma thickened. At maturity containing several white, non-jumping larvae. E. gallicum: Gephyraulus raphanistri
4a Malformations caused by animals => 5
4b Pads of at first closed, glossy, porcelain-like, with mealy dusting sori on various plant parts after rupturing. E. gallicum, nasturtiifolium: Albugo candida
5a Leaf blade with conspicuous, pale green swellings and deflected margins. E. gallicum, abyssinicum: Brevicoryne brassicae
5b Spindle-shaped often deep green swellings on petioles, midrib or stems, up to about 15 mm long. Containing a single larva. E. gallicum, abyssinicum: Ceutorhynchus chalybaeus
5c Leaves clustered on shoot tip or young inflorescences and transformed into a ± fleshy to spongy gall. E. incanum: Contarinia nasturtii