Chapter 21: Heterobasidiomycetes

Heterobasidiomycetes, commonly known as jelly fungi, represent a distinctive group within the Basidiomycota characterized by gelatinous fruiting bodies and unique septal structures including dolipore septa with parenthesomes and septate heterobasidia called phragmobasidia. These fungi are divided into two major subclasses, Heterobasidiomycetidae and Tremellomycetidae, which encompass five primary orders: Ceratobasidiales, Tulasnellales, Dacrymycetales, Auriculariales, and Tremellales. The gelatinous nature of their fruiting bodies provides a remarkable adaptation allowing survival through desiccation and subsequent rehydration, enabling persistence in harsh environmental conditions. Ecologically, these fungi occupy diverse roles as wood-decomposing saprotrophs, mycoparasitic species, mycorrhizal symbionts, and occasionally plant pathogens or medically relevant organisms. Ceratobasidiales are exemplified by Rhizoctonia species, which cause significant agricultural damage including damping-off disease in seedlings and sharp eyespot in cereals, despite forming beneficial orchid mycorrhizal associations that provide essential carbon to developing orchid embryos and protocorms, illustrating the dual nature of fungal interactions. Dacrymycetales produce distinctive yellow-orange gelatinous basidiocarps with forked basidia and include species like Dacrymyces stillatus and Calocera viscosa, which decompose wood and employ heterothallic mating systems with bifactorial control mechanisms. Auriculariales comprise morphologically diverse species with ear- or brain-shaped fruiting bodies, including Auricularia auricula-judae and Exidia glandulosa, and notably include cultivated edible species such as Auricularia polytricha that have been harvested since antiquity in Asia. Tremellales are characterized by yeast-like monokaryotic stages and longitudinally septate tremelloid basidia, with genera including Tremella mesenterica and Tremella fuciformis, the latter being economically important in Asian cultivation for both culinary applications and bioactive polysaccharide production with immunostimulant properties. Understanding heterobasidiomycete diversity reveals the functional significance of morphological innovations and demonstrates how fungi transition between parasitic and symbiotic roles while contributing substantially to nutrient cycling and food production systems globally.