The Phylogeny of Myxomycetes

Abstract Within the myxomycetes, phylogenetic research is still at a relatively early stage; available phylogenies are often based on only a single or a few marker genes. In this chapter, we review the molecular data currently available on the position of myxomycetes in relation to other eukaryotic organisms, and compare these with existing classifications of the group. If the genus Ceratiomyxa is considered separately to all other myxomycetes, the latter are monophyletic. Unambiguously supported by all molecular markers is a split into two basal clades, a dark-spored clade and a bright-spored clade, which is largely in accordance with the traditional classification based on five orders. However, most of these orders are not supported as monophyletic groups, although a new delimitation is difficult due to the low proportion of species hitherto investigated with molecular markers. In the light of molecular data, the traditional criteria used in myxomycete taxonomy have to be reevaluated. The morphology of capillitia and peridia, and especially how these two structures are connected to each other, seems to be highly informative, whereas their presence or absence is not. Similarly, single versus compound fruiting bodies, a character often used to delimit genera, seems to deserve a lower weight, as these structures have evolved several times in parallel. Further research employing molecular markers will most likely lead to a revised hierarchical classification of the myxomycetes.