ABSTRACT
XV. Glaucocystophyta 243
XVI. Chlorophyta 244 A. Pedinophyceae 244 B. Prasinophyceae 245 C. Ulvophyceae 245 D. Chlorophyceae 249 E. Charophyceae 250 F. Zygnematophyceae 252
Acknowledgments 253
References 253
Cell division is an essential aspect of the biology of eukaryotes since it is the structural basis of important phenomena such as growth, development, reproduction, and differentiation. The diversity in the ultrastructural organization of cytokinesis and mitosis is considerable not just among protists,1
but also within individual lineages (phyla, divisions), such as fungi and Chlorophyta. Heath2 listed no less than 54 mitotic characters that are variable in different protistan groups. Yet, his attempt to analyze phylogenetic relationships of 146 organisms representing some 28 higher taxa (including 13 algal divisions) on the basis of these characters was only partially successful.2 One reason was that many mitosis-related characters are difficult to describe in terms of allowing comparison with other organisms. Another problem is the lack of structure-function information. In view of these and other limitations of mitosis as a phylogenetic indicator2 (which also apply to cytokinesis) and because of space constraints, this chapter will not be concerned with elaborate speculations on the phylogeny of major algal groups. The phylogenetic affinities between chromophyte algae (i.e., prymnesiophytes, chrysophytes, diatoms, cryptophytes, phaeophytes, eustigmatophytes, xanthophytes, and raphidophytes) based on evidence from comparative studies of mitosis have been discussed recently by Green.3 Nondividing nuclei will not be described in any detail except when a group of algae is characterized by special ultrastructural nuclear features.
