72 D. M. JOHN, J. H. PRICE, C. A. MAGGS & G. W. LAWSON 



Goniotrichaceae 

 Chroodactylon 



Chroodactylon has usually been referred to in the past as Asterocytis. Drew & Ross (1952) 

 have clearly established that the former is the antedating valid generic name. It has long been 

 suggested that Chroodactylon (as Asterocytis) and Chroothece may well be congeneric (see Pujals, 

 1961, for literature review). More recently, Lewin & Robertson (1971) have demonstrated that 

 the normally filamentous Asterocytis [Chroodactylon] ornata (Goniotrichales) sustains morpho- 

 logical change when cultured at reduced salinities, forming separate unicells in groups and thereby 

 resembling Chroothece (Porphyridiales). Such a relationship, known in various members hitherto 

 placed in the two orders, led Feldmann (1955, 1967) and Dixon (1973) to propose merging the 

 Goniotrichales into the currently accepted Porphyridiales, under the latter name. 



The likelihood is that the species currently known as Asterocytis ornata (C. Ag.) Hamel is 

 correctly placed in the genus now referred to as Chroodactylon. Ardre (4) incorrectly assumed that 

 Drew & Ross (1952) had already made the required combination, but this is not the case. 

 Basson (1979:67) was the first to satisfy all nomenclatural requirements. 



Chroodactylon ornatum (C. Ag.) Basson 

 [As Asterocytis ornata (C. Ag.) Hamel] 

 Canaries (6; 7; 8; 10; 19; 40). 

 [As Asterocytis ramosa (Thwaites) Gobi] 

 Sierra Leone (3). 



Note. Many (see Waern, 1952, for analysis of earlier opinions) have retained the name Astero- 

 cytis [Chroodactylon] ornata for freshwater plants and A. ramosa for plants from marine con- 

 ditions. Presumably this is the basis for retention of A. ramosa in Parke & Dixon's (1976) recent 

 version of the check-list of British marine algae, since the first diagnosis of Asterocytis (as Con- 

 ferva) ornata by C. Agardh (1824 : 104), although brief, is not so inadequate as to be rejected 

 particularly when clearly associated with authentic material, this having been found on examina- 

 tion by Hamel (1924 : 451, 452) to be the same as A. ramosa. Hamel (1924), B0rgesen (6) and 

 Waern (1952), despite the latter's retention of several species names for entries, inclined to the 

 view that one species only is involved in the genus. Lewin & Robertson (1971) showed con- 

 clusively that material (named as A. ornata by them) collected from the seashore at La Jolla, 

 California, could be persuaded to grow in media of one-quarter-strength seawater (but not in 

 lower salinities); they postulated that the occurrence of Asterocytis forms in freshwater may 

 relate to distinct physiological races, if not true species, within the genus. The further establish- 

 ment of the relationship one way or the other requires material from freshwater to be grown in a 

 range of salinities, as well as necessitating the repetition for other geographical areas of the 

 culture experiments of Lewin & Robertson in order to establish that the failure to adapt to 

 freshwater was not merely an aspect of a local physiological race. There seems no clear justifica- 

 tion at the present time for the rejection of the use of the specific epithet ornata for marine 

 material; this, as indicated by Basson (1979:67), is also the earliest name used in connection 

 with the many 'species' of the genus now accepted here as forming a single taxon. 



Goniotrichum alsidii (Zanard.) Howe 



Ascension (unpublished). 



Canaries (19; 29). 



Gabon (31). 



Gambia (33). 



Ghana (29; 34; 41 A). 



Nigeria (29). 



Mauritanie (38). 



Senegal (50). 



Sierra Leone (32). 



Togo (30). 



