238 



L. HILLIS-COLINVAUX 



The Gepps (1911) suggested a common calcified ancestor for the 

 calcareous genera, and devised a separate evolutionary scheme for the 

 non-calcareous members of the group (Section III). This could be part 

 of the scheme proposed below as well, with Udotea, Halimeda, Arabico- 

 dium, Boueina and the other calcareous genera developing from such 

 an ancestor. However, even the limited data we have do not support 

 the rigorous development of calcified and uncalcified taxa from calcified 

 and uncalcified stock respectively. Calcified groups within the marine 

 algae have arisen independently, Padina in the Phaeophyta for 



Penicil lus 



Callipsygma 



Chlorodesmis 



\ 

 Boodleopsis 



t 

 Rhipidodesmis 



Halimeda 



Codium 



Pseudocodium 



Tydemania 



Rhipocephalus 



,1 



Geppella 



Rhipilla 



Fig. 77. Phylogenetic scheme for the Codiaceae proposed by Gihnartin (1966). The 

 genera Udotea and Avrainvillea were considered to be in the Udoteaceae following 

 Nizamuddin (1963), and hence were not included in the scheine. 



example, and calcified and uncalcified phases alternate in the life- 

 cycle of Pedobesia (MacRaild and Womersley, 1974; Section III), and 

 possibly even in Halimeda. Whether or not the juvenile filaments 

 of Halimeda (Section VII) are calcified is not indicated by Meinesz 

 (1972b). 



A more elaborate scheme is presented by Gilmartin (1966) (Fig. 77). 

 He considered Tydemania, with its uniaxial construction, to be a 

 primitive member of the Codiaceae and a connecting Hnk between 

 Rhipocephalus, Halimeda and Penicillus. Recent data have indicated 

 some weaknesses in this scheme, however. It is not supported by wall 

 chemistry, the wall oi Codium, containing mannan while tha,t of Halimeda 

 contains xylan (Parker, 1970). However, in spite of the helpful study 

 of Parker, the data on wall chemistry within the group are scant, and 

 the character may prove not to be a valid one for phylogenetic pur- 

 poses. The scheme is also not supported by plastid structure, with both 

 homoplasty and heteroplasty, and their associated differences, occur- 

 ring in a single evolutionary line {Codium and Halimeda respectively) ; 

 nor is it vindicated on ecological grounds. Gilmartin suggested that 



