Leaf Rust Pathogens on Hypericum pseudohenryi: Describing Melampsora danbaensis sp. nov. and M. hyperici-pseudohenryi sp. nov. from China

Based on morphological and phylogenetic evidence, two novel species of Melampsora were discovered on Hypericum pseudohenryi in China and have been thoroughly characterized. One of these species, designated as M. danbaensis, exhibits distinct features such as aecia of Uredo-type, typically appearing in gregarious or grouped arrangements, and presenting a shallowly pulvinate structure. Aeciospores exhibit tremendous variations in size, ranging in shape from globose to ellipsoidal and bearing pronounced verrucose texture. Telia resemble crusts one-spore deep, covering nearly the entire abaxial leaf surface, with sessile teliospores reaching sizes of up to 65.8 µm, and exhibiting a clavate to cylindrical shape. Another species, designated as M. hyperici-pseudohenryi, is distinguished by Uredo-type uredinia, which are hypophyllous, scattered or grouped, and interspersed with numerous paraphyses. Its urediniospores tend to be globose, ellipsoidal or obovoid, echinulate, and are accompanied by clavate to capitate paraphyses reaching lengths up to 77.6 µm. Phylogenetically, both species form a novel monophyletic clade within the Melampsora genus, with robust support demonstrated by a high Maximum likelihood bootstrap support (MLBS) value of 100% and a Bayesian posterior probability (BPP) of 1. This study enriches our understanding of the diversity and geographical distribution of Melampsora species that infect Hypericum plants in China.