Like other "Puccinia" species, "P. graminis" is an obligate biotroph (it colonizes living plant cells) and has a complex life cycle featuring alternation of generations. The fungus is heteroecious, requiring two hosts to complete its life cycle – the cereal host and the alternate host. There are many species in "Berberis" and "Mahonia" (and their hybrid genus "x Mahoberberis") that are susceptible to stem rust, but the common barberry is considered to be the most important alternate host. P. graminis" is macrocyclic" (exhibits all five of the spore types that are known for rust fungi).