ABSTRACTThe development of the heteroecious, macrocyclic rustPuccinia zoysiaeon zoysiagrasses (Zoysiaspp.) andPaederia scandenswas studied using bright-field and scanning electron microscopy. This fungus grows intercellularly through the mesophyll of the zoysiagrass leaf, invading parenchyma cells, and forming haustoria. However, its growth is restricted by the vascular bundles and the bulliform cells, which the fungus does not penetrate. As a consequence, longitudinal lesions are formed, predominantly on the adaxial leaf surface. Soon after the onset of infection, paraphyses and echinulate urediniospores are produced, and are rapidly exposed due to rupture of the epidermis. Teliospores form later, first within the uredinia, and subsequently in telia which appear on both leaf surfaces. These spores are two-celled, persistent, and pedicellate. They germinated after two months of suspension in water at 4 C, followed by exposure to a saturated atmosphere for 24 hours. Germination begins with the emergence of a basidium (promycelium) from either or both cells of the teliospore. This is followed by the formation of septa and sterigmata from which basidiospores arise. These spores infect leaves ofP. scandens, producing inconspicuous, intercellular spermogonia. Aecia form intercellularly and eventually erupt through the lower leaf surface. The aecial peridium has an unusual double-layered wall, the inner wall of which consists of non-viable aeciospores. Aeciospores are verrucose and are produced in basipetal succession.