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.
Several plant varieties in Berberis and Mahonia (and their hybrid genus x Mahoberberis) are susceptible to stem rust; however, the common barberry (B. vulgaris) is considered the most significant alternate host for these diseases.