Rust on Ground-Ivy Found for the First Time in North America

Ground-ivy or gill-over-the-ground (Glechoma hederacea) is a perennial and a member of the mint family (Lamiaceae). It is characterized by creeping stems that root at the nodes, blue to violet blossoms, and rotund leaves. The plant is native to Eurasia but was introduced to and has become widespread in North America. It is found predominantly in nutrient-rich, shady meadows but also occurs in forests and disturbed habitats. There are several rusts known on G. hederacea in Eurasia. One of them, Puccinia glechomatis, has been introduced to North America. The only two collections of this fungus were made in the United States in August 1998 (near Syracuse University, NY) and in October 1999 (west of West Lafayette, IN) in shady, continuously mowed lawns in private gardens. The specimens were identified by reference to Gaeumann (2) and deposited in the Arthur Herbarium, Purdue University, West Lafayette. P. glechomatis is a microcyclic rust fungus that forms only telia (spore stage III). The sori are up to 1 mm in diameter, forming round cushion-like galls on abaxial leaf surfaces and depressions on adaxial leaf surfaces, opposite galls. The colorless to pale brown teliospore is characterized by its acute apex. Most teliospores germinate immediately and do not function as overwintering spores. It seems likely that the rust species has been in North America for a long time given that the two collections are from widely separated areas. The fungus may have been overlooked. So far, P. glechomatis has been found only on species of the genus Glechoma (including G. urticifolia, which is often placed in the genus Meehania) and seems to be restricted to this genus. The only inoculation experiments made with P. glechomatis proved that the rust does not infect Salvia spp. (sage) (1). There is no evidence that this rust can infect plants indigenous to North America. References: (1) L. Corazza and L. Luongo. Plant Dis. 83:487, 1999. (2) E. G. Simmons. Mycotaxon 37:79, 1990.