Urediniomycetes is a class of fungi primarily known for their role as plant pathogens. They are commonly referred to as rust fungi due to the reddish-brown spores they produce. These fungi typically have complex life cycles that can involve multiple hosts and stages, making them significant in agriculture as they can affect crop yields. The spores of Urediniomycetes are spread by wind and water, allowing them to infect a wide range of plants. Some well-known examples include Puccinia graminis, which causes wheat rust, and Melampsora lini, responsible for flax rust. Understanding these fungi is crucial for managing plant diseases and ensuring food security.