Some Viewpoints on the Phylogeny of Rust Fungi. II. Gymnosporangium

The genus Gymnosporangium is a most noteworthy group among the true aecioid rust fungi.2 Ordinarily these rusts pass their aecial stage on conifers and their teliophase on angiosperms, but Gymnosporangium produces teliospores on Cupressaceae and aecia on the Rosales. The development of cornute and roestelioid aecia is a further new tendency. These aecia have a mechanism which regulates the expulsion of spores in accordance with changing weather conditions. No other plant rust is known to have such an advanced mechanism. Of further interest are the jelly-like matrices in which the teliospores are imbedded. An extensive taxonomic and biologic treatise of the genus Gymnosporangium was written by Kern (13, 14). Numerous further research records published by Dodge (6, 7) and other authors are summarized by Buller (4, pp. 389-414). Despite this intensive study, both the origin of the genus Gymno sporangium and its phylogeny remained rela? tively obscure.