DICTYOSTELIUM AUREO‐STIPES AND DICTYOSTELIUM TENUE: NEW SPECIES OF THE DICTYOSTELIACEAE

Three new cellular slime molds, Dictyostelium aureo-stipes sp. n., D. aureo-stipes var. helvetium var. n. and D. tenue sp. n., are described which possess characteristics heretofore unrecorded in the Dicty,steliaceae. The two species are unlike in dimensions and complexity of form, yet show a number of features in common, and may in fact be closely related. D. aureo-stipes var. helvetium is relatively large and robust, forming multiple-branched fruiting bodies without the regularity of form found in Polysphondylium, yet tending toward symmetry when well-developed. The golden-yellow stipe is a distinguishing feature of D. aureo-stipes and is even more pronounced in var. helvetium. D. tenue is smaller and simpler in form. The degree of branching is much reduced, and oftentimes a solitary sorus terminates a delicate stipe composed of a single tier of cells. Both species are quite sensitive to environmental conditions, particularly temperature, for optimum development occurs within relatively narrow ranges. THE CELLULAR slime molds described herein were first isolated from forest soils twenty years or more ago and are represented in our collections by a substantial number of strains that have been preserved in a lyophilized state. Dictyostelium aureo-stipes was isolated as early as 1942 from soil collected in a hardwood forest near Peoria, Ill. A not uncommon species, it has since been isolated frequently by us and other investigators and was the subject of a short paper by Huffman and Olive (1963) who considered it to be a "variant" of D. mucoroides Brefeld (1869). Other strains obtained from deciduous forests of North America closely resemble the initial isolates. Recently, 1971 to 1977, several strains were isolated from Swiss soils which differ sufficiently from the types found in the deciduous forests of North America to be regarded as a distinct variety, hence designated var. helvetium. The second species, for which the binomial Dictyostelium tenue is proposed, has been known since 1958 when it was isolated from Panama soils collected by Dr. Dietrich Kessler. It was subsequently isolated repeatedly by JCC from tropical and subtropical soils collected in I Received for publication 18 August 1978; revision accepted 24 October 1978. 2 Present address: American Society for Microbiology, 1913 I St. N.W., Washington, D.C. 20006 This work was supported in part by research grant DEB7301510 from The National Science Foundation, and in part from research grant Al 04915 from The National Institutes of Health, U.S. Public Health Service. The writers wish to express their sincere appreciation to Dr. Claude E. Vezina for preparing the Latin diagnoses. Central and South America, East Africa, and Southeast Asia. The first reference to this species was by Cavender and Raper (1968) where it was illustrated and referred to as "D. mucoroides variant." Both species were studied by Norberg (1971) in her comparison of members of the "Dictyostelium mucoroides complex" and tentative descriptions were prepared at that time. A brief paper, published only in abstract form, was presented at the annual meeting of the American Society for Microbiology in Philadelphia in 1972 (Norberg and Raper, 1972). Dictyostelium aureo-stipes is easily recognized because of its yellow sorophores, white sori, and the numerous, irregularly arranged side branches which develop under optimal cultural conditions. The species and the variety helvetium differ from one another is size, aggregative behavior, and optimum temperature ranges. Isolates of the variety are larger and more erect, the aggregates are more stable and uniformly spaced, and the optimum temperature range is lower than for isolates of the species. Dictyostelium tenue is less easily recognized. It suggests D. lacteum van Tieghem (1880) because of the delicate nature of its sorophores; however, its spores are elliptical to reniform while those of D. lacteum are spherical. Superficially it also resembles D. minutum (Raper, 1941) which has elliptical spores, but the sorocarps of that species are generally shorter, less delicate and less flexuous. Both D. aureo-stipes and D. tenue show appreciable variation in size, spore shape, aggre-