THE TYPIFICATION OF THE GENUS NAME ARTHRODESMUS (ALGAE‐CHLOROPHYTA)

Abstract

In a recent paper, Bicudo (1975a) summarizes the story of the generic name Arthrodesmus and concludes that Arthrodesmus Ehr. ex Ralfs is a legitimate genus name in the Desmid family and that it must be typified by A. convergens [Ehr.] Ralfs. This conclusion is based, among other things, on the assumption that the name Arthrodesmus Ehr. (1838) can be ruled out as not validly published, since it was proposed before the starting point of the Desmidiaceae nomenclature (Ralfs, I848). This assumption is correct only if Arthrodesmus Ehr. belongs to the Desmids; therefore, we must first of all typify this name. The name Arthrodesmus was first introduced in the phycological literature by Ehrenberg (1836) as a nomen nudum accompanied by three species names, two of them related to Scenedesmus species, cited without query mark, the third related to the desmid Sphaerozosma elegans, being cited with a query mark, which shows that, from the very beginning, Ehrenberg considered his Arthrodesmus as a new name for Scenedesmus. Arthrodesmus was validly published only two years later (Ehrenberg 1838: I49). In this work, Ehrenberg introduced Arthrodesmus as a new name for Scenedesmus Meyen to which he objected mainly on linguistic grounds. Thus, he discussed at length the meaning and the etymology of the two names and the reasons why he preferred Arthrodesmus. The first three listed species (173 A. quadricaudatus, 174 A. pectinatus, I75 A. acutus) belong actually to the genus Scenedesmus while the following ones (176 A. convergens, 177 A. octocornis and probably 178 A. truncatus) belong to the Desmid family. Of A. convergens Ehrenberg wrote: Sie gehirt vielleicht einer besondern Gattung an, deren Character sich an Euastrum anschliesst, und ist mit den beiden folgenden Arten sehr eng verbunden.. All this shows unequivocally that in Ehrenberg's mind, his new name was first of all a substitute for Scenedesmus. Thus, according to the article 7 of the International Code of Botanical Nomenclature (ICBN, Stafleu 1972), Arthrodesmus Ehr. 1838, published as an avowed substitute for the older Scenedesmus Meyen, must be typified by the type of the older name, namely by one of the five species cited by Meyen in his original description of the genus (1829: 774). As the starting point for the nomenclature of the group of algae to which Scenedesmus belongs is May i, 1753, we must consider that the name Arthrodesmus Ehr. 1838 was validly published, even if it is an illegitimate superfluous synonym of Scenedesmus. Consequently, the desmid genus name Arthrodesmus Ralfs 1848, typified by A. convergens [Ehr.] Ralfs is illegitimate, being a later homonym of Arthrodesmus Ehr. 1838; it must be rejected even if the earlier homonym is illegitimate and superfluous (ICBN, art. 64). Retention of the name Arthrodesmus Ralfs for a genus of Desmids could be effected only by conservation, but it does not seem very advisable to conserve this name for the following reasons: i. There is no general agreement among desmidiologists on the circumscription of Arthrodesmus and on its typification: Teiling (1948, 1967) and Bourrelly (1966: 432) exclude from this genus all the monospinous (i.e. with one spine at each angle) species allotted