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. In spring, these germinate to produce basidiospores that infect yellow starthistle rosette leaves. The rust then develops through two subsequent spring spore stages (pycniospores and aeciospores). Symptoms include yellowish chlorotic lesions with raised centers which turn into orangish-brown or rusty-brown pustules that produce large amounts of urediniospores. The spores are microscopic. The urediniospores spread rapidly from plant to plant as they are easily dispersed by both wind and rain. Multiple “generations” of uredinia infection can occur during the spring and summer, with each full cycle taking two weeks to complete; however, the spores require at least 8 hours of dew to germinate.