EM Fungi Fruiting in Dicymbe Forests – the “Elevated Fruiting Phenomenon”

Ectomycorrhizal (EM) fungi commonly fruit above the forest floor in Dicymbe corymbosa forests

Due to the complex reiterative morphology of mature D. corymbosa trees, large amounts of litter and humus accumulate aboveground on the pseudotrunks and root mounds. These litter accumulations are permeated by adventitious Dicymbe roots and ectomycorrhizas (Woolley et al., 2008; Henkel, 2003). Many EM fungal species can be found fruiting from these elevated organic soils. However, a distinct assemblage of species appear to fruit exclusively from root mounds and may be “obligate elevated fruiters.”

Non-subiculate Elevated Fruiters

These “elevated fruiters” include species in which no specialized subiculum structure is formed – the basidiomata arise directly from the humic deposits (e.g. Tylopilus exiguus, Boletellus ananas var. ananas, Boletellus dicymbophilus, Boletellus exiguus, Cantharellus atratus, Inocybe epidendron, Inocybe pulchella, Russula campinensis) (Mayor et al., 2008; Fulgenzi et al., 2008; Matheny et al., 2003; Henkel et al., 2000; Henkel, 1999).

Subiculum-forming and Resupinate Elevated Fruiters

Other species form a semi-perennial subiculum from which multiple flushes of basidiomata arise (e.g. Lactarius panuoides, L. brunellus, L. multiceps, L. subiculatus nom. prov.) (Miller et al., 2002; Henkel et al., 2000). Additionally, subiculate and resupinate EM taxa “climb” living tree seedlings via rhizomorph ascension, forming basidiomata 20–30 cm above ground on stems, leaves, branches, and fallen logs (e.g. pleurotoid Russulaceae, Tomentella and Sebacina morphospecies – Miller & Henkel, 2004, Henkel et al., unpublished data).

Long Stalks and Stipes to Escape Saturated Soils

Pseudotulostoma volvata (Elaphomycetaceae) forms Epigeous ascomata with the spore-bearing gleba elevated on a stalk > 5 cm above ground level, from which spore dispersal occurs via rain splash during the height of the wet season. This is significant because the closest relatives of Pseudotulostoma are Elaphomyces spp., vertebrate-dispersed false truffles that fruit belowground (Henkel et al., 2006; Miller et al. 2001). Many other agarics that fruit directly from the forest floor have grossly accentuated stipe lengths, such as Cortinarius aff. violaceous (20–30 cm or more). The propensity for elevated fruiting across genera may represent adaptations for effective rainy season spore dispersal given the highly saturated conditions of the forest floor.


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