XVI International Botanical Congess

Two species of pleurotoid basidiomycetes previously described in Lactarius sect. Panuoidei were redescribed from fresh material collected in Guyana. Similarities between cystidia in the pileipellis and hymenium and the mantle of co-occurring ectomycorrhizae suggested an ectomycorrhizal nutritional mode for L. panuoides and L. campinensis. Analysis of DNA sequences in the nLSU gene region taken from fruitbodies and co-occurring ectomycorrhizae confirm an ectomycorrhizal habit. The fruiting habit of these fungi on organic deposits and well-rotted wood at elevated positions is not due solely to saprotrophy. Analysis of ITS+LSU rDNA sequences indicates that these pleurotoid fungi share close affinities with established sections of the genus Lactarius, regardless of the unusual morphology of their basidiomata. Discussion is provided for Pleurogala, erected to accommodate lignicolous, pleurotoid species of Lactarius.