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 haven¹t 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]

WordNet (r) 3.0 (2006):

Uredinales
    n 1: rust fungi: parasitic fungi causing rust in plants;
         sometimes placed in [syn: Uredinales, order Uredinales]