Traditional morphology-based taxonomy of dictyostelids is rejected by molecular phylogeny. A new classification is presented based on monophyletic entities with consistent and strong molecular phylogenetic support and that are, as far as possible, morphologically recognizable. All newly named clades are diagnosed with small subunit ribosomal RNA (18S rRNA) sequence signatures plus morphological synapomorphies where possible. The two major molecular clades are given the rank of order, as Acytosteliales ord. nov. and Dictyosteliales. The two major clades within each of these orders are recognized and given the rank of family as, respectively, Acytosteliaceae and Cavenderiaceae fam. nov. in Acytosteliales, and Dictyosteliaceae and Raperosteliaceae fam. nov. in Dictyosteliales. Twelve genera are recognized: Cavenderia gen. nov. in Cavenderiaceae, Acytostelium, Rostrostelium gen. nov. and Heterostelium gen. nov. in Acytosteliaceae, Tieghemostelium gen. nov., Hagiwaraea gen. nov., Raperostelium gen. nov. and Speleostelium gen. nov. in Raperosteliaceae, and Dictyostelium and Polysphondylium in Dictyosteliaceae. The "polycephalum" complex is treated as Coremiostelium gen. nov. (not assigned to family) and the "polycarpum" complex as Synstelium gen. nov. (not assigned to order and family). Coenonia, which may not be a dictyostelid, is treated as a genus incertae sedis. Eighty-eight new combinations are made at species and variety level, and Dictyostelium ammophilum is validated.

Aim The goal of this project was to compile, organize, and present the known distributional data on the dictyostelid cellular slime moulds (CSMs) found in forest soils worldwide. The question of what factors influence CSM distribution patterns was also addressed.Location CSMs have been recovered from soils of temperate deciduous forest, tropical deciduous and seasonal evergreen rainforest, boreal coniferous forest, and tundra by various investigators around the world.Methods Within each of these four biomes, various locations around the world have been sampled by a number of investigators. The current study attempts to synthesize the known dictyostelid distributional data and present specific patterns of distribution.Results Worldwide, sixty-five species of CSM were found to occupy various forest soils. These species' distributions fell into one of four categories: cosmopolitan, disjunct, restricted, and pantropical.Main conclusions Global CSM distribution patterns are influenced by a variety of factors other than the biota (including but not restricted to climate, latitude, altitude, soil pH, and soil-forming parent materials). The current study supports the thesis that organic inputs from specific plant associations and animal vectors have an important role as well.

In late Jan and early Feb 2005 samples for isolation of dictyostelid cellular slime molds (dictyostelids) were collected in five different provinces and from six national parks (all located 39-55°S) in Patagonia and Tierra del Fuego, Argentina. Southern beech (Nothofagus) forests represented the primary vegetation type investigated, but some samples were obtained from Patagonian steppe, alpine meadows, Valdivian temperate rainforests and coniferous forests dominated by Araucaria, Austrocedrus and Fitzroya. Among the dictyostelids isolated from the samples we collected were seven species new to science. These species (Dictyostelium austroandinum, D. chordatum, D. fasciculoideum, D. gargantuum, D. leptosomopsis, D. valdivianum and Polysphondylium patagonicum) are described herein on the basis of both morphology and molecular (SSU rDNA) data. One of the new species, D. gargantuum, is one of the largest representatives of the group reported to date. Another unusual species, D. chordatum, produces long interwoven sorocarps that do not appear to respond to a spacing gas similar to the condition first noted in D. implicatum.

During the period of February to April of 1998, soil/litter samples for isolation of dictyostelid cellular slime moulds were collected throughout New Zealand. Collecting sites included examples of main forest types found in the country and a range in latitude (35°S to 47°S) that encompassed most of New Zealand. Thirteen species of dictyostelids were recovered; all of these occurred at low frequencies and densities. This total included a number of species (e.g., Dictyostelium mucoroides and Polysphondylium violaceum) that are common and widespread throughout the Northern Hemisphere as well as several other species that have a more restricted distribution. Among the latter are Dictyostelium fasciculatum, not previously known outside of Europe, and D. rosarium, previously reported from only a few scattered localities in the Northern Hemisphere. Five of the species recovered (D. antarcticum, D. australe, D. leptosomum, D. quercibrachium, and P. anisocaule) are described for the first time. New Zealand is the most isolated land mass of its size in the world, and the assemblage of dictyostelids present is quite distinctive and seems to reflect this isolation.