There are many species in Berberis and Mahonia (and their hybrid genus x Mahoberberis) that are susceptible to stem rust, but the common barberry (B. vulgaris) is considered to be the most important alternate host.
There are many species in Berberis and Mahonia (and their hybrid genus x Mahoberberis) that are vulnerable to stem rust, but the common barberry (B. vulgaris) is regarded as the most crucial alternate host.