XVI International Botanical Congess

The members of the genus Acytostelium of the Acytosteliaceae are the smallest Dictyostelids, characterized by slender acellular sorophores which support very small globose sori. They inhabit surface humus and leaf mold of forests soils and have been widely isolated from different forests of the world. Ten taxa have been recovered since Raper first isolated A. letosomum from hardwood forest of Illinois in 1952 A. elipticum was first discovered in 1968 by Cavender from tropical forests in Trinidad while A. subglobosum was isolated in 1970 from forests in S. E. Asia. A. irregularosporum was isolated in 1971 by H. Hagiwara from deciduous forest of Japan. Six additional species and a variety of A. leptosomum are presented as new to science, all were isolated since 1990 and all but one from tropical environments. They are: A. digitatum, from semi-evergreen rain forest at Tikal, Guatemala, A. aggregatum and A. coronatum, from tropical rain forest of the Peruvian Amazon, A. leptosomum var. decumbens, from a Mayan milpa in Belize, the largest, A. magnuphorum, from a bog in Ohio, A. reticulatum, from lower montane forest of Loquillo Nat'l For. , Puerto Rico, and the smallest, A. minutissimum, isolated by J. Landolt and S. Stephenson, from elfin woodland of a volcano in Costa Rica