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From The Collaborative International Dictionary of English v.0.48:
Uredinales \Uredinales\, prop. n. pl. (Biol.) An order of fungi of the phylum Basidiomycota, comprising the rust fungi. [PJC] The order Uredinales includes between an estimated 5,000 and 7,000 species of diverse plant pathogens. They have been around since the Carboniferous Age (250-300 million years ago), and were well established on the very first ferns. Members of Uredinales are well enough adapted that they inhabit every continent except for Antarctica. Commonly known as the "rust fungi," they attack nearly all types of plant life, and are economically devastating to many crops. Members of Uredinales have a very diverse and complex life cycle-that may affect more than one host family and include up to five different stages. Morphological Features: Uredinales includes both autoecious and heteroecious parasites. Autoecious genera infect only one plant host, while heteroecious genera carry out different parts of their life cycle on two different hosts. One example of a heteroecious fungus, Puccinia graminis, the black stem rust of wheat, requires both the barberry bush and a grass to complete its complicated life cycle. Life cycles of Uredinales are very diverse and complex. Some genera have up to five stages of their life cycle: Spermagonia, Aecia, Uredinia, Telia, and Basidia. Spores are produced in each stage with differing ploidy: spermatia (n), aeciospores (n+n), unidiniospores (n+n), teliospores (n+n to 2n), and basidiospores (n). Genera that do not exhibit all five of these stages either show three or four instead. Ecology: Uredinales comprise the most devastating plant pathogens of all Basidiomycota. Genera of Uredinales are responsible for diseases such as: coffee rust, cedar-apple rust, black stem rust of cereals, carnation rust, and peanut rust. There are thousands of other rusts that havenšt been listed that are also responsible for being seriously detrimental to many genera of plants. Despite all of the ecological problems that these fungi cause to plants, recent efforts have attempted to use some of these rusts to control weedy pests. --Kari Jensen (University of Wisconsin, course material) [available at: http://botit.botany.wisc.edu/courses/Botany_332/uredinales.html] [PJC]