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Remarks (public):This genus is close to Thanatephorus, Uthatobasidium, Cejpomyces and Botryobasidium. The spore repetition distinguishes it from the two last genera. From the two others, it is recognized by the rounded shape of the basidia and by the nature of the hymenium. The basidia
originate on the basal hyphae or on short sidebranches. They do not form a regular palisade as in Thanatephorus and Cejpomyces. The production of secondary spores (repetition) occurs in a minority of spores. This character is usually looked upon as systematically important, indicating a relationship with the Heterobasidiomycetes. The repetition is in itself easily interpreted as a delayed ability of the protoplasm to produce a sterigma. This ability is normally found only in the protoplasm of the basidium, but in some cases this ability remains even when the protoplasm has entered the spore. Some spores adhering to the hymenium (e.g. during the drying of a collected specimen) show repetition, but it is doubtful whether this is the normal procedure in nature. It has been suggested that the ability to repeat could be of importance for a redistribution of spores fallen on unfavourable substrate, but it is doubtful if this is really the case.
It cannot be excluded that the protoplasm of thinwalled spores sticking to the fruitbody, are induced to produce sterigmata by active substances excreted from the basidia. In gelatinous fruitbodies where spore repetition generally occurs, there are interhyphal liquids that may be of importance as carriers of such exudates.
In Ceratobasidium it is observed that adventitious septa sometimes occur in the sterigmata. This too has been regarded as an indication of relationship with the Heterobasidiomycetes. Comparison is made with the sterigmatic septum in Tulasnella or with the basidial septa in Tremellaceae and Heterobasidiomycetes in general. However, such adventitious septa can be found in many resupinate Hymenomycetes even in sterigmata if they are sufficiently large. Such sterigmatic septa can be seen in Tomentella, Hyphoderma, Hypochnicium a.o. As soon as there is a difference in plasm-density in a cell, such septation can be expected. Consequently, it cannot therefore be used as a criterion of a close relationship. The swollen sterigma of Tulasnella have been compared with the large and stout sterigma of Ceratobasidium, the reason for this genus being transferred to the Tulasnellaceae. The swollen sterigmata of Tulasnella seem rather to be a specialized character in which the protoplasm is prepared for the spore formation, just as in the four cells of the septated Tremella basidium. The Ceratobasidium sterigmata though larger, are more comparable with the normal sterigmata in the Corticiaceae, Thelephoraceae etc. For the time being it seems wiser to place Ceratobasidium in the Corticiaceae
than in the Tulasnellaceae. However, there is no doubt that Ceratobasidium because of the shape of the basidium (probasidium) as well as sterigmata, belongs in the periphery of the family and rather close to the Tremellaceae. The borderline between this family and the Corticiaceae is vague,
but to us it seems unnatural to place genera like Ceratobasidium, Cejpomyces, Thanatephorus and Botryobasidium in different families, why we place them all in Corticiaceae. A possible alternative could be to arrange them in a family of their own even if little is gained by this.
In Northern Europe only four species of Ceratobasidium are found. Three others are known, one of which is parasitical on higher plants (C. anceps (Bres. & Syd.) Jacks.), one has very long sinuous spores (C. calosporum Rogers) and one has subglobose spores (C. obscurum Rogers). Corticium terrigenum Bres., previously placed in Ceratobasidium, is referred to Cejpomyces, and C. sterigmaticum Bourd. to Thanatephorus.
 
Description:Ceratobasidium Rogers - Univ. Iowa Studies 17:4, 1935
Fruitbody very thin, smooth, when fresh waxy (ceraceous), when dry forming mostly not more than a greyish bloom on the substrate, hyphae without clamps, the basal ones with somewhat thickened walls, mostly about 5 µm wide, no cystidia, basidia from short perpendicular hyphal branches or directly from the basal hyphae, basidia mostly subglobose, with 2-4 stout, cornute sterigmata, 10-20 µm long, spores of the Scandinavian species ellipsoid to ovate to suballantoid, sometimes producing secondary spores from a sterigma of varying length.
Genotypus: Ceratobasidium calosporum Rogers.
 
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