| Rust fungi in the genus Chrysomyxa (Uredinales, Coleosporiaceae) occur in boreal forests of the Northern Hemisphere on conifers (mostly Picea spp.) and alternate to members of the Ericaceae sensu lato, especially Rhododendron (including Ledum). The 19 recognized species occurring in North America and Europe were studied by light and scanning electron microscopy, and, where possible, field observations and inoculation experiments. Detailed, fully illustrated descriptions are given, including taxonomic history, life cycle, and economic importance. In addition to host specificity, morphological characters useful in delineating species are size and surface morphology of aeciospores and urediniospores, including shape and size of warts and presence and nature of a longitudinal groove or cap, and morphology of the aecial peridium. North American rusts formerly considered varieties of the European C. ledi are recognized as distinct species: C. nagodhii on L. groenlandicum and L. decumbens, C. neoglandulosi on L. glandulosum, and C. vaccinii on Vaccinium parvifolium. A new small-spored species, C. reticulata, infecting L. groenlandicum and cultivated rhododendrons in North America is described. A new anamorphic species that lacks spermogonia and likely belongs to Chrysomyxa is described from coastal British Columbia as Peridermium zilleri. Chrysomyxa ledicola is shown to vary with location in urediniospore and aeciospore size, the presence of a narrow flat area on spores, and the presence of spermogonia.;Methods for DNA extraction and amplification of the ITS region of ribosomal DNA were investigated. Direct sequencing of ITS region amplification products was not possible, suggesting the existence of variation among ITS repeat units within an individual.;The biology of selected species was elucidated experimentally. The life cycle of C. woroninii was confirmed by inoculation of basidiospores from L. groenlandicum onto spruce needles. Field observations and experiments with Pyrola asarifolia infected with C. pirolata showed that moisture is an important factor in the induction of telia on Pyrola leaves. The autoecious North American spruce rust, C. weirii, was investigated for morphology, spore dispersal and germination, and cytology. The monokaryotic teliospores are diaspores that germinate in free water to form a two-celled basidium and two tetranucleate basidiospores. Water dispersal of teliospores has not previously been reported in Chrysomyxa. |
