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.

Neonectria fuckeliana (C. Booth) Castl. & Rossman is known to be associated with a stem canker disease of Pinus radiata D. Don in New Zealand plantation forests. Although N. fuckeliana has been previously recorded as a wound invader or weak pathogen of Picea and Abies species in the Northern Hemisphere, little is currently known about the basic biology of the fungus. This paper outlines early investigations into the spore production and dispersal of N. fuckeliana in New Zealand. Perithecia of N. fuckeliana occur frequently on pruned stubs and on the surface of cankers, and ascospores appear to be the primary means of dispersal for this fungus in New Zealand. Both field collections and spore trapping show that mature perithecia contain viable ascospores in all seasons, and spores are ejected and dispersed using moisture. The conidial phases are rarely found in the field. Optimum temperature for both growth of mycelium and ascospore germination was between 15 and 25 °C. Some spore germination occurred at temperatures as low as 5 °C, but above 25 °C spore germination was abnormal. Ascospores and perithecia favoured storage in lower temperatures: overall, ascospores from perithecia stored at room temperature gradually lost their viability, whereas those stored at 4 and –8 °C maintained their viability over an 18 month period.

Many rust fungi (Uredinales) that infect rhododendrons are difficult to identify because of similar spore size and overall morphology. As part of a morphological study of rusts in the genus Chrysomyxa, herbarium specimens of Asian rhododendron rusts were examined by light and scanning electron microscopy. They were compared with similar taxa from Europe and North America. Revised and illustrated descriptions are provided for the uredinia and telia of Chrysomyxa dietelii and Chrysomyxa succinea; details of the conspicuous uredinial peridium of both species are described for the first time. A new genus and species, Diaphanopellis forrestii, is proposed to accommodate a rust fungus with uredinia covered by a peridium of ornamented cells (Aecidium-type) and teliospores enclosed in transparent outer sheaths. This species includes the previously described anamorphs Aecidium rhododendri and A. sino-rhododendri. Three new anamorphic species with unique urediniospore morphology also are described: Caeoma clemensii from Philippines, Caeoma spinulospora from Tibet, and Caeoma yunnanensis from Yunnan, China. For morphological and nomenclatural reasons Uredo rhododendri ('rhododendronis') is renamed as Caeoma dumeticola and Uredo rhododendri-capitati is transferred to Caeoma. A key to Asian rhododendron rusts that form uredinia is provided. In general morphological groups of rhododendron rusts correlate with the subgenera of Rhododendron on which they occur, suggesting coevolution of these parasites with their hosts.