species on : species delineation, diversity and host alternation.

species (, , ) are the causal agents of cedar-apple rust diseases, which can lead to significant economic losses to apple cultivars. Currently, the genus contains 17 described species that alternate between spermogonial/aecial stages on species and telial stages on or species, although these have yet to receive a modern systematic treatment. Furthermore, prior studies have shown that does not belong to the sensu stricto (s.str.), nor is it allied to any currently defined rust family. In this study we examine the phylogenetic placement of the genus We also delineate interspecific boundaries of the species on based on phylogenies inferred from concatenated data of rDNA SSU, ITS and LSU and the holomorphic morphology of the entire life cycle. Based on these results, we propose a new family, , to accommodate the genus , and recognize 22 species parasitic on species, of which , , , and are new. Typification of , , , , , and are proposed to stabilize the use of names. Morphological and molecular data from type materials of 14 species are provided. Finally, morphological characteristics, host alternation and geographical distribution data are provided for each species on .