2011), and are more likely to be adaptive than many morphological features used in agaric systematics. Ecology may therefore provide informative selleckchem synapomorphic characters if new nutritional strategies were the foundation of adaptive radiations. Hence, we summarize results of studies on the ecology of genera in Hygrophoraceae below, with emphasis see more on nutritional strategies. Hygrophorus s.s. represents an independent evolutionary acquisition of the ectomycorrhizal lifestyle in basidiomycete fungi (Tedersoo et al. 2010), though recent micromorphological

evidence indicates the relationship in H. olivaceoalbus may be parasitic rather than mutualistic (Agerer 2012). Individual species of Hygrophorus s.s. are considered host specialists but this has only been definitively shown for a handful of species (Jacobsson and Larsson 2007; Larsson and Jacobsson 2004; Molina et al. 1992). Thus they represent an adaptive radiation within Hygrophoraceae. Species of Hygrophorus s.s. fruit primarily in undisturbed forest habitats dominated by ectomycorrhizal (ECM) plants (Visser 1995; Singer 1949).

While the genus has long been considered PF-4708671 symbiotic with roots (e.g. Frank 1888; Noack 1889), Kropp and Trappe (1982) provided definitive proof when they synthesized ECM of Hygrophorus purpurascens in pure culture with Tsuga heterophylla. More recently, molecular methods have confirmed the presence of Hygrophorus species on the roots of both angiosperms and gymnosperms from a variety of habitats in Amrubicin the Northern Hemisphere (see Online Resource 2). According to Hobbie and Agerer (2010), species of Hygrophorus s.s. form “contact”, “short”, or “medium-smooth” exploration-type ECM that are hydrophilic and lack rhizomorphs. The restricted soil volume exploited by Hygrophorus ectomycorrhizae may explain why some species are considered “nitrophilic” and respond positively to high nitrogen inputs (Lilleskov et al. 2001, 2002; Vineis et al. 2010) and why some respond negatively to liming (Kjøller and Clemmensen 2009; Pena et al. 2010).

In addition to limitations of potential benefits to the host from Hygrophorus mycorrhizae due to limited soil exploration by the fungus, Agerer (2012) showed that the intracellular development of H. olivaceoalbus in Picea roots was characteristic of a parasitic infection. Proliferation of H. olivaceoalbus in defensive tannin droplets within host cells was also consistent with the high activity of phenoloxidase (Agerer et al. 2000) and laccase (Agerer 2012) in that species. Further evidence for parasitic rather than mutualistic association comes from the low isotopic ∂15 N of H. olivaceoalbus basidiomes (−3.6—0.1 % in Taylor et al. 2003; 2.7 ± 3.5 % in Trudell et al. 2004), which is generally below the range of ∂15 N found in typical ectomycorrhizal fungal basidiomes (3—18 % ∂15 N, Taylor et al. 2003; Trudell et al. 2004; Agerer et al. 2012; Seitzman et al. 2011).