CLASSIFICATION OF THE ALGAE' 



By GEORGE F. PAPENFUSS 



University of California, Berkeley 



Introduction 



A GENERAL TREATMENT of sucli a hetcrogeneoiis assemblage of organisms as the 

 algae may fittingly be introduced with a statement of the criteria used in the 

 delimitation of the group. 



These plants are readily separated from those next above them in the evo- 

 lutionary scale, the archegoniate plants, by the fact that their reproductive or- 

 gans lack a primarily produced sterile jacket of cells. (The antheridium of the 

 Charophycophyta is an exception.) The separation of some algae from certain 

 members of the other groups of simple organisms, such as the bacteria, the 

 fungi, and the protozoa, is much more difficult and not infrequently the as- 

 signing of an organism to the algae or to one of these groups is a purely arbi- 

 trary procedure. 



Although the major taxa of algae show little or no relationship to one an- 

 other, the group as a whole is clearly distinguished from other simple organ- 

 isms by the ability of a great majority of the species to synthesize organic 

 compounds by the process of photosynthesis. There are many exceptions to this 

 rule but the saprophytic, parasitic, or holozoic forms usually reveal their al- 

 liance to autotrophic types by their structure, life history, and storage products. 

 In very many instances the heterotrophic forms appear to have been derived 

 from photosynthetic types. The autotrophic bluegreen algae may be distin- 

 guished from the autotrophic bacteria by their possession of chlorophyll a and 

 the evolution of oxygen as a by-product of photosynthesis. 



In modern systems of classification the algae comprise more than half the 

 number of plant phyla. Of the known species, however, they constitute less 

 than 10 per cent. The disproportionately large number of major algal taxa 

 reflects the great diversity in the structure, reproduction, and metabolism of 

 these plants as contrasted with the remainder of the plant kingdom. 



Within the confines of this brief treatment, my review of the history of the 

 classification of the group of necessity will be confined to the broad outlines of 

 the system. Attention will also be given to the history of the discovery of sex 

 in the algae and to the growth in knowledge of their life histories since ad- 

 vances in these aspects of phycology have almost always contributed to a better 

 understanding of the interrelationships and phylogeny of the groups concerned. 



The nomenclature of the majority of algae, like that of most plant groups. 



1. I am deeply indebted to Dr. Johannes Proskauer for critically reading the manu- 

 script and for his many constructive suggestions. I should also like to thank Professor 

 G. M. Smith and Dr. T. V. Desikachary for kindly reading the manuscript and making 

 helpful suggestions. 



[115] 



