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The species of Niesslia including anamorphs formerly known as Monocillium form a distinct group in the Hypocreales and can be delimited by several unique morphological characters. Niesslia species inhabit decaying plant substrates, such as leaf litter or bark of diverse plants, especially coniferous hosts. Certain species occur on and may parasitize lichens, fruiting bodies of other fungi and even nematode eggs. Taxonomically, species of Niesslia are classified in the Niessliaceae. Niesslia species are recognised by their tiny superficial, mostly dark brown, shiny and typically spine covered ascomata. Monocillium-like phialides formed in situ and in culture are usually partly or entirely thick-walled. Phialides with wall thickening only in their basal parts sometimes expand in width to taper again into a conidiiferous neck, while others terminate in a non-sporulating vesicle. Based on the revised generic concept presented here, Niesslia accommodates 50 cultured species plus around 40 species known only from herbarium material. Some of the latter species may eventually have to be excluded from Niesslia but are maintained in the genus ad interim, until DNA sequences necessary for their accurate reclassification are available. The taxonomic concept based on morphological characters is corroborated by DNA sequences of phylogenetic marker loci such as the large subunit (28S) of the ribosomal RNA gene, internal transcribed spacer regions 1 and 2 including the 5.8S ribosomal RNA gene, and partial sequences of translation elongation factor 1-α, β-tubulin 2 and γ-actin genes. These DNA barcodes support most of the morphologically delimited species and the generic concept of Niesslia.

Unlike most phialide-producing fungi that liberate a multiplicity of conidia from each conidiogenous cell, only single conidia are formed on phialide-like conidiogenous cells in Aphanocladium, Verticimonosporium, and some species of Sibirina. A group of isolates obtained from soil of native Artemisia tridentata (sagebrush) grassland in Wyoming and from desert soil in Iraq is compared with these genera and classified as a fourth genus, Stanjemonium, honouring Stanley J. Hughes. Phylogenetic analyses of partial nuclear small- (18S) and large-subunit (28S) rDNA sequences indicate that Stanjemonium spp. form a monophyletic group with Emericellopsis. Sequences from the nuclear 18S and 28S rDNA were too conserved to resolve morphological species of Stanjemonium; however, phylogenetic analysis of b-tubulin and translation elongation factor 1a gene exons and introns resolved all species distinguished morphologically. Numerous conidiogenous cells or denticles are scattered along the cells of aerial hyphae in Aphanocladium and Stanjemonium spp., very rapidly collapsing into denticles in the former, somewhat more persistent and leaving broad scars in the latter. In Cladobotryum-Sibirina and Verticimonosporium spp., conidiogenous cells are discrete in terminal and intercalary whorls; phialides of the latter taxon are particularly swollen. The taxonomy of Aphanocladium is not yet resolved. Two species are recognized in Verticimonosporium. Three new species of Stanjemonium are described, and one new combination from Aphanocladium is proposed, along with one new species of Cladobotryum.Key words: Aphanocladium, Cladobotryum, conidiogenesis, hyphomycetes, molecular phylogeny, phialide, Stanjemonium, systematics, Verticimonosporium.

During 2005 and 2006, eight declining, mature Fagus sylvatica trees with severe crown dieback were encountered at two stands near Ljubljana and Kamnik in central Slovenia. Bleeding cankers were seen mostly in the lower parts of the stem. Fresh cankers showed orange brown necroses of the inner bark and cambium. Older cankers were dark brown and surrounded by cracks and shedding bark. Small pieces of marginal tissue were excised from fresh necrotic lesions and incubated in the dark at 20°C on P5ARP and cornmeal (CMA) agar plates. Soil samples collected from around the base of these declining trees were submerged in sterile distilled water. Leaves of Rhododendron catawbiense were used as bait to test for the presence of Phytophthora spp. Several similar isolates were obtained from trees and soil from both stands. Colonies were narrowly petaloid, slow growing on P5ARP, and fast growing on CMA. The colonies produced abundant sporangia when submerged in pond water. Semipapillate, noncaducous sporangia were ovoid to obpyriform, but were occasionally distorted, and 30 to 69 (49) μm long and 23 to 44 (34) μm wide. Neither hyphal swellings nor chlamydospores developed. Isolates were homothallic showing paragynous antheridia, spherical oogonia of 22 to 31 (25) μm diameter, and plerotic oospores of 20 to 27 (23) μm diameter. The morphological characters resembled those described for Phytophthora citricola (1). ITS rDNA, spanning ITS 1 and 2, plus the 5.8S rDNA were generated using primers ITS4 and ITS5. Isolates from symptomatic trees and the soil yielded identical sequences and were the same as various sequences deposited for P. citricola at GenBank. The ITS rDNA of one representative strain was deposited at GenBank (Accession No. EF423556). Mycelial plugs from one of the P. citricola strains grown on CMA were used to inoculate stem wounds of seven potted seedlings and wounds made on four freshly cut, healthy branches of F. sylvatica. Sterile agar plugs were used as controls. The test was carried out over 4 weeks at 20°C. Extensive necrotic lesions developed around inoculation points on seedlings and branches, whereas the controls showed no symptoms. P. citricola could also be reisolated from margins of these lesions. During the past decade, declining F. sylvatica trees were observed in an increasing number of stands in Germany (2). Several Phytophthora species appeared to be involved in this decline, but P. citricola was the most frequently recovered species (2,3). To our knowledge, this it the first report of P. citricola found associated with a decline of European beech in Slovenia. References: (1) D. C. Erwin and O. K. Ribeiro. Pages 282–287 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) T. Jung. Forst Holz. 60:131, 2005. (3) T. Jung et al. Mycologist 19:159, 2005.