276 



BIOCHEMICAL SYSTEMATICS 



clearly recognized as speculative and evaluated accordingly. As in- 

 dicated in Table 14-1 the distribution of carotenoid pigments among 

 the algal groups does not provide any obvious indications of relation- 

 ships among the groups. Goodwin (1962), who discussed the compara- 

 tive biochemistry of carotenoids, constructed a hypothetical evolu- 

 tionary scheme for the Protista based on carotenoid pigments (Fig. 

 14-1). However, he notes that the scheme "may have Httle contact 

 with reahty but insofar as it stimulates biologists to attempt to fill in 

 the gaps which have been indicated in our knowledge of carotenoid 

 distribution, then it will have served its purpose." 



Recently, Dougherty and Allen (1960) discussed the phylo- 

 genetic relationships of the bacteria and algae. The first evolutionary 

 level is considered by these authors to be represented by bacteria 

 and blue-green algae, the second level by the red algae, and the third 

 level by other algal groups. By this scheme, the red algae are assumed 

 to have arisen from blue- green algae and in turn to have given rise to 

 the green algae, and possibly independently, to other groups of algae. 

 Higher plants presumably arose from green algae. Dougherty and 

 Allen, and also Goodwin (1962), view the carotenoid (and chlorophyll) 

 pigment distributions as generally in agreement with the broad scheme 

 described above. At least, the data are not considered to be incompat- 

 ible with the scheme proposed. Similarly, a number of alternative 

 schemes might be accommodated by the data, for the evidence con- 

 sists principally of partial overlaps in pigment complement among 

 the various groups, and therefore a taxonomic treatment is subject to 

 various permutations. As stated by Goodwin such schemes are valuable 

 in stimulating future research, but they are not intended to encourage 

 any taxonomic dogma. 



Another group of pigments related to foHc acid, the pteridines, 

 comprise a potentially systematically useful group. So far, pteridines 

 are definitely found, outside of certain animal groups, in bacteria, 

 fungi, and certain blue-green algae, but they are suspected to occur in 

 higher plants (Wolf, 1960). Hatfield et al. (1961) have found that the 

 pteridine, biopterin, which occurs in many blue-green algae as a glyco- 

 side, is associated with a number of different sugars among different 

 species, though the glycoside of a particular species is apparently 

 constant. These authors suggest that a further study of specific 

 glycosides of various algal species would be of taxonomic interest. 



Betacyanins: A group of pigments known as betacyanins^ 

 provides one of the best available illustrations of the vahdity of 



2 This name was proposed by Dreiding (1961) in an important review of these 

 compounds. The yellow pigments, presumed to be of the same type, are called betaxan- 

 thins. Both occur as glycosides. 



