Systematics of pleurotoid Russulaceae from Guyana and Japan, with notes on their ectomycorrhizal status

Three species of pleurotoid, putatively lignicolous basidiomycetes previously described in the genus Lactarius sect Panuoideiwere redescribed from fresh material collected in Guyana and Japan. In Guyana, Lactarius panuoides and Lactarius campinensis were restricted to forests dominated by ectomycorrhizal Dicymbe species (Caesalpiniaceae) and basidiomata of both pleurotoid species were subtended by ectomycorrhizal rootlets. This suggested an ectomycorrhizal nutritional mode for these fungi. Analysis of DNA sequences in the nuclear large subunit region taken from basidiomata and co-occurring ectomycorrhizae of L. panuoides and L. campinensis confirmed that these fungi are ectomycorrhizal and that their fruiting habit on organic deposits and well rotted wood at elevated positions is not due to saprotrophy, as previously assumed. Lactarius uyedae was collected in Japan from mature temperate forests dominated by Fagaceae, yet ectomycorrhizal rootlets were not found in association with the basidiomata. Morphological features and analysis of DNA sequences suggested that L. panuoides and L. uyedae have affinities with established sections of the genus Lactarius, regardless of the pleurotoid morphology of their basidiomata, and that L. campinensis should be transferred to the genus Russula. Discussion is provided for the genus Pleurogala, which was erected to accomodate putatively lignicolous, pleurotoid species of Lactarius.