The class Pucciniomycetes is a group of fungi within the phylum Basidiomycota, primarily known for including rust fungi, which are important plant pathogens. Members of this class are obligate parasites, meaning they require living plant tissue to complete their life cycles. They exhibit complex life cycles that often involve multiple spore types and sometimes alternate between two different host plants. Morphologically, Pucciniomycetes produce specialized structures called haustoria to extract nutrients from their hosts. Economically and ecologically, they are significant because rust diseases can cause major crop losses and affect natural ecosystems, but they also serve as models for studying host-pathogen interactions and coevolution.