Critical assessment of the Lactarius gerardii species complex (Russulales) Dirk STUBBE*, Jorinde NUYTINCK, Annemieke VERBEKEN Research Group Mycology, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium a r t i c l e i n f o Article history: Received 21 August 2009 Received in revised form 21 December 2009 Accepted 11 January 2010 Available online 2 February 2010 Corresponding Editor: Joseph W. Spatafora Keywords: Biogeography Cryptic species Ectomycorrhiza Lactifluus Phylogeography a b s t r a c t This paper investigates species delimitation within the Lactarius gerardii species complex and explores its taxonomic and geographical extent. A combined molecular phylogeny based on ITS, LSU and rpb2 gene sequences is constructed and morphological characters are evaluated. While L. gerardiiwas originally described from North America, it has later been reported from all over Asia. Therefore a worldwide sampling range was aimed at, including species exhibiting morphological affinities with L. gerardii. The phylogenetic analyses indicate that intercontinental conspecificity in L. gerardii is absent. Thirty strongly supported clades are retrieved of which 18 are morphologically identifiable species. The group is elevated to Lactarius subg. Gerardii stat. nov. It includes, apart from L. gerardii s.l., L. atrovelutinus, L. bicolor,L. ochrogalactus, L. petersenii, L. reticulatovenosus, L. sepiaceus, L. subgerardii and L. wirrabara, as well as the pleurotoid L. uyedae. The paraphyletic nature of the genus Lactarius is confirmed. Lactarius subg. Gerardii appears not affiliated with L. subg. Plinthogalus and this can be substantiated morphologically. No representatives are known from Europe, Africa or South America. The high frequency of intercontinental sister relationships observed between America, Asia and the Australian region, suggests multiple migration and speciation events have occurred across continents. ª 2010 The British Mycological Society. Published by Elsevier Ltd. All rights reserved. Introduction Lactarius,also known as the genus of the milkcaps, exhibits the characteristic feature of exuding a latex-like substance when injured. The genus has a subcosmopolitan distribution and is one of the main ectomycorrhizal symbionts in many species of former R. subsect. Ochricompactae ( Buyck et al. 2008). While the remainder of Russula appears monophyletic, the results of Buyck et al. (2008) also indicate that Lactarius should be further split up into two separate genera, with one genus containing L. subgenera Russularia, Piperites and Plintho- galus and the other containing L. subgenera Lactarius, Lactifluus j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u n b i o f u n g a l b i o l o g y 1 1 4 ( 2 0 1 0 ) 2 7 1 – 2 8 3