Puccinia monoica, Rust Fungus

"Puccinia monoica is a rust fungus of the genus Puccinia that inhibits flowering in its host plants (those of the Arabis genus) and transforms host behavior in order to facilitate sexual reproduction to pass on its genes. Infection occurs when the fungus sends its throughout the stem of the mustard plant, siphoning off some of the nutrients of its host. However, to reproduce, Puccinia monoica must exchange genes with the Puccinia inside another mustard plant. The fungus sterilizes the plant, preventing it from sending up its own flowers. Instead, the fungus forces the infected plant to turn clusters of its leaves into brilliant "flowers" (pseudoflowers)." From Wikipedia.

Photographed (macro) this infected Rock Cress (?) plant at 12-Mile Coulee, Calgary, on 1st May 2009. It's an interesting thing to see and quite attractive.