An ex-type culture cannot always tell the ultimate truth

An ex-type culture cannot always tell the ultimate truth

This note is prompted by the case of the generic name Ochroconis, a rather common genus of saprotrophic soil hyphomycetes, some of which grow occasionally on humans and fish. Von Arx, in the 1970s, being mainly interested in producing keys to identify fungal genera in culture morphologically, did not believe that Scolecobasidium terreum E.V. Abbott 1927 with Y-shaped yellowish conidia, and other species of this genus with darker, unbranched conidia were congeneric, as proposed by Barron & Busch (1962). Therefore, he let his young staff member G. Sybren de Hoog describe a separate genus, Ochroconis, for the latter, larger group (de Hoog & von Arx 1974). In addition to mycologists who regarded the similar colony characters and rhexolytic conidial liberation of all species involved as significant (e.g. Ellis 1971, 1976, Domsch et al. 1980), molecular findings (Horré et al. 1999, Machouart et al. 2014) have clearly shown this generic separation to be unwarranted. In addition two faster-growing halophilic species, S. salinum and S. arenarium were included in the genus by Ellis (1976), but they are now rightly excluded again and classified in Paradendryphiella Woudenb. & Crous 2013 (Woudenberg et al. 2013). The probable extype culture of S. terreum, CBS 203.27, no longer sporulates and phylogenetically falls outside the genus. It no longer shows the features that the ex-type would be expected to support, a misfortune that sometimes happens with a culture after decades of preservation.

Other comparable cases are Acremonium domschii W. Gams 1971, a species originally described as closely related to the anamorph of the species now named Cosmospora viridescens (C. Booth) Gräfenhan 2011 (Gräfenhan et al. 2011), but lacking green pigmentation; the ex-type culture of Gams’ name, CBS 764.69, however, now shows a fungus unrelated to Cosmospora and therefore that species name was omitted in the cited paper. Monocillium arctiicola W. Gams 1971 was described by Gams (1971) as characterized by rather large conidia, but the ex-type culture, CBS 994.69, now has narrow conidia and is unrelated to other isolates accurately matching the description of this species. The dried type culture still shows the correct fungus and DNA sequences of the other isolates representing this species can be taken as correct.

Unfortunate consequences arise when a wrongly identified fungus is designated as an epitype of a species, as happened with Hypocrea farinosa Berk. & Broome 1851 for which Overton et al. (2000) designated an epitype without studying the extant holotype. It was left to Jaklitsch et al. (2008) to correct the situation and to resurrect the generic name Protocrea Petch 1937 for this fungus and its relatives, while Overton et al.’s fungus is now known as Hypocrea decipiens Jaklitsch et al. 2008.

Sybren de Hoog, in order to retain the generic name Ochroconis, let his student K. Samerpitak declare Scolecobasidium a dubious genus, because the identity of the type was uncertain to them (Samerpitak et al. 2014), in spite of many reliably named cultures of S. terreum being available all over the world, which clearly define the identity of this characteristic fungus. One of these cultures discovered by Domsch et al. (1980) was the CBS 510.71 ex-type of Humicola minima Fassat. 1967, whose author had not seen the characteristic Y-shaped conidia that were formed on certain media by the original culture. Without mentioning the source of this informtion, Samerpitak et al. (2014) made the combination Ochroconis minima (Fassatiová) Samerp. & de Hoog 2014, which would have to replace Scolecobasidium terreum. Needless to say, Ochroconis has not been recognized by Seifert et al. (2011). In the era ofproduction of lists of fungal names for protection, the responsible committee should not be misguided and recognize the incorrect name for this genus.

Thanks to David L. Hawksworth for helpful suggestions.