Phylogenie and phylogeographie van de Russulaceae

Introduction

With more than 1200 accepted species (out of more than 3000 species described), the Russulaceae is one of the largest families of ectomycorrhizal fungi that play a dominant role in many vegetations worldwide. Historically, the core of this family consists of two genera: Lactarius and Russula. Both were described more than two centuries ago from Europe as easily recognizable, agaricoid genera.

The research group Mycology at the Ghent University studies the genus Lactarius since more than 10 years. Insights and concepts in the Russulaceae have changed profoundly during this period.

• Traditional, angiocarp and pleurotoid genera are synonymised: Typical agaricoid and gymnocarp  forms (with cap, stipe and gills) have evolved several times into angiocarp (entirely closed, truffle-like) or pleurotoid (with laterally attached stipe) fruiting bodies. We were the first to describe angiocarp species in the genus Lactarius, based on morphological and molecular evidence (Eberhardt & Verbeken, 2004, Nuytinck et al., 2004). Within Lactarius s.l. there are angiocarp species in at least five large clades. Pleurotoid species are less frequent within Lactarius and Russula, but also evolved more than once within each genus.

• Russula and Lactarius are subdivided into four genera: Molecular phylogenetic analyses based on multiple genes show that four clades can be distinguished within the agaricoid Russulaceae: the genus Lactarius, although morphologically easily recognizable in Europe, is polyphyletic (Buyck et al., 2008). The new genus Multifurca was proposed to accommodate representatives of Russula subsection Ochricompactae, where some rare representatives of both genera are united in one well-supported clade. The description of this new genus is a first step in the obvious choice not to lump Lactarius and Russula in one big genus Russula, but to split up in four smaller genera. For Lactarius this means that the subgenera Lactariopsis, Lactifluus, Edules and Lactarius will be united in the genus Lactifluus (Buyck et al., 2009).


• Some morphological characters that traditionally were considered as phylogenetically informative, appear not to be so: Most striking is the inclusion of L. porninsis, a species with white latex, in Lactarius section Deliciosi which is particularly known for its bright coloured latex (orange, red, blue). An other example is Lactarius section Colorati, where all species have a similar pileipellis-type (trichoderm) and a felty to squamulose cap. The section  now turns out to be polyphyletic. In Lactifluus, the several, large and very similar species with a white pileus and acrid latex appear to be distantly related (Lactifluus vellereus-group vs. Lactifluus piperatus-group).

• Agaricoid and resupinate (crust-like) genera are closely related within the Russulaceae: The delimitation of the family Russulaceae revealed that some resupinate Russulales (Boidinia, Gloeopeniophorella) are much closer related to agaricoid forms than previously supposed (Larsson & Larsson, 2003; Miller et al., 2006).

Goals

We are currently working on the following topics arising from the new insights explained above:

• Phylogeny: The genus Lactifluus consists mainly of tropical species, many of which are still lacking in our phylogenetic studies. We demonstrated that the diversity within Lactifluus is much more complex than previously assumed and the preliminary results strongly suggest that a thorough study of this genus, using multiple genes, could uncover the basal relationships between the genera in the Russulaceae. Another unsolved question is whether some of the observed morphological resemblances between Lactarius, Lactifluus and Russula can be supported molecularly, as was done for Multifurca.
• Phylogeography: What is the most ancient group and where did the family Russulaceae originate? How have milk caps and russulas spread over the earth? When did the genera in the Russulaceae diverge? How did the current species distribution areas evolve and is there a co-evolutionary pattern discernable with their symbiotic partner?
• Comparative phylogeny: How fast do Lactarius, Lactifluus, Russula and Multifurca evolve molecularly and morphologically when compared to each other? How can we understand the morphological evolution of these agaricoid genera from corticioid forms (Boidinia, Gloeopeniophorella)? Which factors promote the process of becoming angiocarp? What did the ancestor of the Russulaceae of the agaricoid Russulaceae look like?

References

Buyck B., Hofstetter V., Eberhardt U., Verbeken A. & Kauff F. (2008) Walking the thin line between Russula and Lactarius: the dilemma of Russula sect. Ochricompactae. Fungal Diversity 28: 15-40.
Buyck B., Hofstetter V., Verbeken A. & Walleyn R. (2009) Proposal to conserve Lactarius nom. cons. (Basidiomycota) with a conserved type. Taxon 58(2).
Eberhardt U. & Verbeken A. (2004) Sequestrate Lactarius species from tropical Africa: L. angiocarpus sp. nov. and L. dolichocaulis comb. nov. Mycological Research 108: 1042-1052.
Larsson L. & Larsson K-H. (2003) Phylogenetic relationships of russuloid basidiomycetes with emphasis on aphyllophoralean taxa. Mycologia 95: 1037-1065.
Miller S.L., Larsson E., Larsson K.H., Verbeken A. & Nuytinck J. (2006) Perspectives in the new Russulales. Mycologia 98: 960-970.
Nuytinck J., Verbeken A., Delarue S. & Walleyn R. “2003” (2004) Systematics of European sequestrate lactarioid Russulaceae with spiny spore ornamentation. Belgian Journal of Botany 136(2): 145-153.