Heterobasidiomycetes

Heterobasidiomycetes, including jelly fungi, smuts and rusts, are basidiomycetes with septate basidia. This contrasts them to homobasidiomycetes (alternatively called holobasidiomycetes), including most mushrooms and other Agaricomycetes, which have aseptate basidia. The division of all basidiomycetes between these two groups has been influential in fungal taxonomy, and is still used informally, but it is no longer the basis of formal classification. In modern taxonomy homobasidiomycetes roughly correspond to the monophyletic class Agaricomycetes, whereas heterobasidiomycetes are paraphyletic and as such correspond to various taxa from different taxonomic ranks, including the Basidiomycota other than Agaricomycetes and a few basal groups within Agaricomycetes.

In addition to having septate basidia, heterobasidiomycetes also frequently possess large irregularly shaped sterigmata and spores that are capable of self-replication - a process where a spore, instead of germinating into a vegetative hypha, gives rise to a sterigma and a new spore, which is then discharged as if from a normal basidium. In contrast, homobasidiomycetes, in addition to having aseptate basidia, generally have small regularly shaped sterigmata and spores that do not self-replicate. In different classifications, different features have been stressed.

Certain taxa, such as Dacrymycetaceae, Ceratobasidiaceae or Tulasnellaceae, due to possessing a combination of hetero- as well as homobasidiomycetous features, have been difficult to definitively assign to either group, resulting in dissenting opinions among taxonomists. For example, Dacrymycetaceae possess very large and irregularly shaped sterigmata as well as self-replicating spores, but have aseptate basidia. Tulasnellaceae have self-replicating spores and grossly swollen sterigmata that are separated from the basidium with a septum at the base, however the basidial body itself is not septate and the sterigmata and the basidium are quite regularly shaped. Ceratobasidiaceae have aseptate basidia, but the sterigmata are quite large and irregular and the spores are self-replicating.

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