Clumps of irregular swellings and distortions affecting all parts of a single branch of a stem, smooth and hairless in spring but apparently drying to a rough and irregular brown in the fall. Observed on Sisymbrium irio, Brassica nigra, and other Brassicaceae native to Eurasia.

Per the discussion here, this galling is in most cases caused by Peronosporomycetes, mainly Hyaloperonospora and Albugo. At least some of the Sisymbrium galls have been tentatively idenitified by Senna Robeson as caused by Hyaloperonospora sisymbrii-loeselii, and Gallformers now has a page for this gall.

Four of the 32 observations tagged with GF code "sisymbrium-broom-swelling" had insects or exit holes associated with the galls, and it was suggested that a beetle might be the inducer. More specifically, it was suggested that a weevil, Ceutorhynchus chalybaeus, which sometimes causes stem swellings, might account for at least part of the galling. However, the theory that the weevil was the gall inducer did not account for all of the distortions, and those who tentatively suggested the weevil ID seemed to recognize this.