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The traditional classification of the Myxomycetes (Myxogastrea) into five orders (Echinosteliales, Liceales, Trichiales, Stemonitidales and Physarales), used in all monographs published since 1945, does not properly reflect evolutionary relationships within the group. Reviewing all published phylogenies for myxomycete subgroups together with a 18S rDNA phylogeny of the entire group serving as an illustration, we suggest a revised hierarchical classification, in which taxa of higher ranks are formally named according to the International Code of Nomenclature for algae, fungi and plants. In addition, informal zoological names are provided. The exosporous genus Ceratiomyxa, together with some protosteloid amoebae, constitute the class Ceratiomyxomycetes. The class Myxomycetes is divided into a bright- and a dark-spored clade, now formally named as subclasses Lucisporomycetidae and Columellomycetidae, respectively. For bright-spored myxomycetes, four orders are proposed: Cribrariales (considered as a basal group), Reticulariales, a narrowly circumscribed Liceales and Trichiales. The dark-spored myxomycetes include five orders: Echinosteliales (considered as a basal group), Clastodermatales, Meridermatales, a more narrowly circumscribed Stemonitidales and Physarales (including as well most of the traditional Stemonitidales with durable peridia). Molecular data provide evidence that conspicuous morphological characters such as solitary versus compound fructifications or presence versus absence of a stalk are overestimated. Details of the capillitium and peridium, and especially how these structures are connected to each other, seem to reflect evolutionary relationships much better than many characters which have been used in the past.

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Based on morphological investigations and a phylogeny constructed with partial sequences of the SSU rDNA gene, we revalidate the genus Alwisia and propose the combination Alwisia bombarda Berk. & Broome to be used against Tubifera bombarda (Berk. & Broome) G.W. Martin. Two new species, Alwisia morula and A. repens, are described based on material collected respectively in Costa Rica and Australia. Both new species lack a capillitium and possess individually stalked subspherical sporothecae. Alwisia repens differs from A. morula by its procumbent stalks and iridescent peridium. A comparison of 83 sequences of species in the genera Lycogala, Reticularia and Tubifera with a recent two-gene phylogeny of the bright-spored myxomycetes resulted in a similar topology of both Bayesian and maximum likelihood trees and placed A. bombarda, A. morula and A. repens in one well delimited clade within Reticulariaceae.

Based on a combination of morphological and molecular investigations, a critical revision of the widely distributed myxomycete Tubifera ferruginosa is presented. A phylogeny of the morphospecies, based on partial 18S nuc rDNA sequences, displays several clearly distinct clades, all differing by a genetic distance (p distance) of at least 0.15, with the distance within the clades below 0.11. These molecular differences correlate with morphological characters, such as the shape of sporothecal tips, the color of immature fructifications and the ultrastructure of the inner surface of the peridium. The combination of morphological and molecular data provides evidence that T. ferruginosa is actually a species complex, representing at least seven species. These are T. ferruginosa sensu stricto, T. applanata, T. corymbosa, T. dudkae, T. magna, T. montana and T. pseudomicrosperma. Among these T. applanata and T. dudkae (as Reticularia dudkae) were described recently based on morphological characters and the 18S nuc rDNA phylogeny confirmed their separation. Another four species, T. corymbosa, T. magna, T. montana and T. pseudomicrosperma, are described here. We propose an epitype for T. ferruginosa sensu stricto and recognize subsp. ferruginosa and subsp. acutissima within this species. All studied taxa of the T. ferruginosa complex are shown to lack a capillitium. Structures formerly described as capillitium represent the hyphae of fungi occurring within the fructifications.

Tubifera applanata sp. nov. is proposed to validate "Tubulifera applanata" nom. inval. The species diagnosis and some notes on its morphology are provided. At 0.40−0.65 mm diam., individual sporothecae are somewhat larger than in T. ferruginosa and T. microsperma and smaller than those in T. casparyi. Circular ornamentations on the inner peridial surface in T. applanata are larger than previously noted, reaching a size up to 2.9 μm.

Abstract:A new species of myxomycete, Perichaena longipes, is described from 56 specimens of fruiting bodies that appeared in moist chamber cultures prepared with samples of decaying plant materials collected in Panama, Costa Rica and Brazil. This new species is distinguished from the morphologically similar species P. pedata on the basis of the much longer stipe, lighter peridium and the unique ornamentation of the capillitium. The nuc 18S ribosomal DNA sequences obtained from four specimens of P. longipes support the distinction of this new taxon and its separation from P. pedata. Furthermore, maximum likelihood phylogeny supports earlier evidence that species currently within the genus Perichaena do not form a monophyletic clade.Instead they appear to form three separate branches within the bright-spored clade. The first clade includes P. longipes together with several species of Trichia and Metatrichia, the second includes P. pedata and P. chrysosperma, and the third clade is composed of P. corticalis, P. depressa and P. luteola.

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