Chloridium virescens and Helicosporium virescens, binominals for different fungi based on the same basionym Dematium virescens

It has come to our attention (Morgan-Jones et al., 1991) that two names based on a single basionym are currently in use for different fungi. These are Chloridium virescens (Pers.) W. Gams & Holubovfa-Jechovaf (1976) and Helicosporium virescens (Pers.) Sivanesan (1984). Both are based upon Dematium virescens Persoon (1794). The fungi to which they have been applied are the anamorphs of Chaetosphaeria vermicularioides (Sacc. & Roum.) W. Gams & Holubovfa-Jechovf and Tubeufia cerea (Berk. & Curt.) Hohnel, respectively (Gams and Holubovi-Jechovf, 1976; Sivanesan, 1984). This is an unacceptable nomenclatural situation that requires resolution. Correct application of the basionym Dematium virescens, either as Chloridium virescens or Helicosporium virescens, revolves around its typification. In that, there is some difficulty. Gams and Holubovfa-Jechovfa (1976), in their revision of the genus Chloridium Link, took up Dematium virescens as an earlier name for Chloridium viride Link (1809). Prior to 1976, the name C. viride had been in widespread use for the type species of Chloridium, as seen in Saccardo (1886), Hughes (1958), Barron (1968) and Ellis (1971). Link (1809) had regarded C. viride and D. virescens as different since he classified the latter in his genus Sporotrichum Link, as S. virescens (Pers.) Link. Both Persoon (1822) and Link (1824), however, considered each other's species as being the same. Streinz (1862) listed D. virescens as a synonym of C viride. In contrast, Saccardo (1886) treated the two separately. Gams and Holubovf-Jechovf (1976) pointed out that the epithet 'virescens Pers.' had been given preference over 'viride Link' as the earliest available name by Fries (1832). The only specimen labelled D. virescens in Persoon's herbarium at Leiden (L) (910.255-753) bears no Chloridium but an abundance of Helicosporium vegetum Nees, the type species of Helicosporium Nees. Herein lies the problem. This material was examined by Hughes (1958) and by Gams and Holubovf-Jechovf (1976). The former author, in his list of names to be excluded from Dematium Pers., indicated D. virescens to be the Helicosporium state of Ophionectria cerea (a synonym of T. cerea), a logical judgement on the basis of the presence of that anamorph on the D. virescens specimen in the Persoon collection. Sivanesan (1984) made the recombination Helicosporium virescens for the anamorph of T. cerea, listing Helicosporium vegetum as a facultative synonym without any word of explanation. Persoon's generic diagnosis of Dematium reads 'sporulis globosis aut ovalibus' which brings into serious question whether the specimen labelled Dematium virescens, cited above, present in Persoon's herbarium, is the type. Since H. vegetum, being helicosporous, is a very different-looking fungus morphologically, it seems possible that Persoon mistakenly placed the name D. virescens on the material. Persoon (1822), incidentally, knew of the existence of H. vegetum. Had Persoon seen conidia of H. vegetum it seems unlikely that he would have named his specimen D. virescens. A superficial resemblance, including greenish coloration, may have led Persoon to confuse the one with the other and misapply his