New species of dictyostelid cellular slime moulds from Australia John C. Landolt A , James C. Cavender B , Steven L. Stephenson C,E and Eduardo M. Vadell D A Department of Biology, Shepherd University, Shepherdstown, West Virginia 25443, USA. B Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701, USA. C Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA. D Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento Ciencias Biologicas -- Pabellon II, 1428 Buenos Aires, Argentina. E Corresponding author. Email: slsteph@uark.edu Abstract. During the 2001--2006 field seasons, samples for isolation of dictyostelid cellular slime moulds were collected at several localities in Queensland, the Northern Territory, Western Australia and Victoria. The majority of these samples were collected from the soil--litter layer on the ground, but some additional samples were obtained from the layer of organic matter (‘canopy soil’) associated with the bases of vascular epiphytes on the trunks and branches of trees in the tropical forests of northern Queensland. Many of the forms recovered from these samples could be assigned to described taxa, including such cosmopolitan species as Dictyostelium mucoroides, Polysphondylium pallidum, P. violaceum and D. giganteum. However, several others appear to represent new species, and eight of these (D. boomeransporum, D. flexuosum, D. granulosum, D. myxobasis, D. radiculatum, D. rotatum, P. australicum and P. stolonicoideum) are described herein. The large number of apparently undescribed forms suggests that the dictyostelid biota of Australia is relatively distinct when compared with that of any other continent. Introduction Dictyostelid cellular slime moulds (dictyostelids) are single- celled, eukaryotic, phagotrophic bacterivores usually present and often abundant in terrestrial ecosystems. These organisms represent a normal component of the microflora in soils and play a role in maintaining the natural balance that exists between bacteria and other microorganisms in the soil environment. For most of their life cycle, dictyostelids exist as separate, independent, amoeboid cells (myxamoebae) that feed on bacteria, grow, and multiply by binary fission. When the available food supply within a given microsite becomes depleted, numerous myxamoebae aggregate to form a structure called a pseudoplasmodium, within which each cell maintains its individual integrity. The pseudoplasmodium then produces one or more fruiting bodies (sorocarps) bearing spores. Dictyostelid fruiting bodies are microscopic and rarely observed except in laboratory culture. Under favourable conditions, the spores germinate to release myxamoebae, and the life cycle begins anew (Raper 1984). The continent of Australia, with a total extent of ~7 682 300 km 2 , covers ~5% of the earth’s land area. Most of the continent is low, flat and dry; deserts, dry grasslands and woodlands are the predominant vegetation types. There have been few reports of dictyostelids from Australia. In an unpublished MSc thesis, Robson (1978) reported eight different forms that were recovered from samples collected in New South Wales, the Australian Capital Territory and Queensland. These consisted of a member of the D. mucoroides complex, D. minutum, D. purpureum, a form similar to D. lacteum, an unknown form suggestive of D. polycephalum, another unknown form with brown pigmentation, Polysphondylium pallidum and P. violaceum. Later, Hohl (pers. comm. with J. Landolt) isolated three species (D. mucoroides, P. pallidum and P. violaceum) from samples collected in Queensland. In what apparently represents the first publication dealing specificially with Australian dictyostelids, albeit not from the continent itself, Stephenson et al. (1998) reported D. mucoroides var. stoloniferum from subantarctic Macquarie Island. Collectively, these studies provided relatively little data on the distribution and occurrence of dictyostelids in Australia. The primary objective of the present study was to carry out surveys for these organisms at several localities throughout the continent in an effort to develop the first appreciable body of information on what is an understudied group for this region of the world. Materials and methods The surveys that yielded the records reported in the present paper were carried out during a period extending from May 2001 to March and April of 2004, with a few additional samples obtained in June 2006. Samples were collected from more than 30 localities and/or habitats that represented a variety of different vegetation types in Queensland, the Northern Territory, Western Australia and Victoria. Particular emphasis was placed on the tropical forests of northern Queensland. The majority of samples were collected from the soil--litter layer on the ground, but some additional samples were obtained from Ó CSIRO 3 April 2008 10.1071/SB07040 1030-1887/08/010050 CSIRO PUBLISHING www.publish.csiro.au/journals/asb Australian Systematic Botany, 21, 50--66