Ceraceosorales is a monotypic order in Ustilaginomycotina. Its namesake, Ceraceosorus bombacis, was described as a phytopathogen of Bombax ceiba in India. In this study, we describe Ceraceosorus guamensis sp. nov., collected on the South Pacific island of Guam, which appears to represent the second isolation of any member of this order in over 40 years. Ceraceosorus species are monokaryotic and filamentous in culture, producing conidia on potato dextrose agar. However, both species behave yeast-like when cultured on corn meal agar. The internal transcribed spacer (ITS) region (spanning the ITS1-5.8S-ITS2) in both species of Ceraceosorus is highly heterogeneous containing multiple disparate copies that can vary intragenomically by up to 3.5 %. Moreover, this region could not be amplified using the fungal ITS primers most frequently used for culture-independent methods of assessing fungal biodiversity. This fact, combined with the extremely slow growth rates on commonly employed media, may indicate that members of this lineage are potentially underdetected by current sampling methods.
Keywords: Exobasidiomycetes; Mariana archipelago; Metagenomics; Rare fungi; Smut fungi; rDNA.