This fungus has a complicated life cycle that includes five different spore stages throughout the year. Teliospores can withstand freezing temperatures and are the overwintering stage. Teliospores germinate in spring, leading to the production of basidiospores that infect musk thistle plants in the early rosette and bolting stages. The rust then develops through two subsequent spring stages (pycniospore [presumed] and aeciospore). Symptoms include reddish-brown pustules that produce large amounts of urediniospores. Urediniospores are microscopic, golden to dark brown, flat, round, and have short spines covering their surface. Urediniospores spread rapidly from plant to plant as they are easily dispersed by both wind and rain, allowing multiple “generations” of uredinia infection to occur during the spring and summer.