Heterothallic mating systems in the Echinostelium minutum complex

Six cultures of an Echinostelium sp. slime mold were isolated from cholla cactus detritus collected in Death Valley National Park, California. All six isolates are heterothallic and belong to a single, multiple-allelic mating series with four known mating types. Although the spores, stalks and columella of these isolates resembled a reduced E. minutum, the nearly complete absence of a capillitium prevents a definitive identification. A seventh isolate from cholla collected near Tucson, Arizona and identified as a small desert form of E. minutum, also is heterothallic, but does not cross with the first mating series. This is the first detailed description of a heterothallic mating system in the Echinosteliales.