Species diversity, taxonomy, and phylogeny of <i>Gymnosporangium</i> in China

<i>Gymnosporangium</i> is a group of plant fungal pathogens that cause rust diseases on many economically important fruit trees. Most <i>Gymnosporangium</i> are heteroecious and demicyclic, producing four morphologically diverse spore stages on two taxonomically unrelated host plants, the Cupressaceae and Rosaceae. The complex life cycle and heteroecism make it difficult to investigate the species within <i>Gymnosporangium</i>. To determine the taxonomy, phylogeny, and species diversity of <i>Gymnosporangium</i> in China, a large collection of 672 specimens were analyzed using a combination of morphological observations and phylogenetic analyses. In total, 27 <i>Gymnosporangium</i> species from China are documented here, including 22 known species, one new combination, one new record, and three new species. The study also documents a novel aeciospore surface structure with an irregular surface that is described here as “surfy.”