Puccinia monoica

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 fugus sends its tendrils throughout the stem of the mustard plant, siphoning off some of the nutrients that the flower obtains from the sky and the soil. However, to reproduce, Puccinia monica must have sex 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--but fake-- flowers.

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These imitations are identical to other flowers found on the mountains of Colorado, where the mustard plant is found, not only in visible light but also in ultraviolet light. Since bees "see" in the ultraviolet range, these flowers are more attractive to the pollinating insects. In addition, the fungus produces a distinct scent that to attract insects; this olfactory appeal has allowed the fungus to evolve and "improve" upon the mimicry system by facilitating proper transfer of fungal spermatia and pollen. (Roy, B.A. and Raguso, R.A. Olfactory versus visual cues in a floral mimicry system. Oecologia, V. 109, No. 3: 414-426) The bees feed on a sweet, sticky substance that the fungus forces the plant to produce on the imitation flowers. The fungus forces its sperm and its female sex organs into them, so that the bees can fertilizethe fungus as they travel from plant to plant. (Zimmer, C. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures.)