Morphology, taxonomy, and nomenclature of the<i>Chrysomyxa ledi</i>complex and related rust fungi on spruce and Ericaceae in North America and Europe

Abstract

Rust fungi in the genus Chrysomyxa Unger occur in boreal forests of the northern hemisphere on Pinaceae (mostly Picea A. Dietr.), and most species alternate to angiosperm hosts in the Ericaceae. About 30 species are known worldwide. Although several species are economically important pathogens of spruce and rhododendrons, knowledge about species delineations, relationships among species on different continents, and life cycles is lacking. A group of species with similar spore size, including the Chrysomyxa ledi de Bary complex, was re-examined using field observations, inoculation experiments, and light and scanning electron microscopy. In addition to host specificity, characters found useful in species delineation were urediniospore and aeciospore size and shape, and ornamentation of spores and the aecial peridium. Detailed descriptions are given for eight Chrysomyxa species, including synonyms, types, distribution, relationship to other species, and disease impact. The members of the C. ledi complex are considered separate species: Chrysomyxa ledi on Ledum palustre, Chrysomyxa nagodhii sp.nov. on Ledum groenlandicum and Ledum decumbens, Chrysomyxa neoglandulosi sp.nov. on Ledum glandulosum, Chrysomyxa cassandrae on Chamaedaphne calyculata, Chrysomyxa rhododendri on Rhododendron spp., and Chrysomyxa vaccinii comb.nov. on Vaccinium parvifolium. Chrysomyxa chiogenis, with similar spore size, is included for comparison. A previously unrecognized small-spored species, Chrysomyxa reticulata sp.nov., is described on Ledum spp. and Rhododendron spp. Evidence is presented that C. reticulata spreads from native Ledum spp. in North America to cultivated rhododendrons. A new anamorphic species, Peridermium zilleri, likely belonging in Chrysomyxa, is described on Picea sitchensis from coastal British Columbia.Key words: Uredinales, Rhododendron, needle rust, Ledum, systematics.