Phakopsora hornotina, an additional autoecious rust species on Meliosma in the Philippines and the Ryukyu Islands, Japan

• Aecidium hornotinum is the spermogonial–aecial anamorph of Phakopsora hornotina.
• Phakopsora hornotina occurs on Meliosma aff. multiflora and M. arnottiana subsp. oldhamii.
• Phakopsora hornotina is distributed in the Philippines and the Ryukyu Islands, Japan.

Aecidium hornotinum, originally described for a fungus on Meliosma aff. multiflora from the Philippines, has been reported to occur on M. arnottiana subsp. oldhamii (=M. rhoifolia) in southern islands of Kagoshima and Okinawa (the Ryukyu Islands), Japan. The taxonomic identity of the Aecidium fungus on M. arnottiana subsp. oldhamii distributed in the Ryukyu Islands to A. hornotinum was confirmed by morphological comparison with the type material of A. hornotinum. Field observations in several islands of Okinawa and an examination of herbarium specimens showed a possible life cycle connection between A. hornotinum and a uredinial–telial fungus reported as Phakopsora meliosmae in the Ryukyus. Experimental inoculations with basidiospores and aeciospores proved the autoecious, macrocyclic life cycle of the rust fungus. This fungus was found distinct in sorus and spore morphology and host preference from P. meliosmae on M. myriantha. Thus, a new holomorph name, Phakopsora hornotina, was proposed for this fungus.