While differing opinions on supraordinal classification of red algae would seem to be irrelevant to this catalogue, decisions must be made as to whether any such classification is used, and if so, which one. Heretofore, the chief consideration has been whether all red algae should be placed in one class coextensive with a division and divided into two subclasses or whether the two subclasses should be elevated to the rank of class, the two resulting classes comprising a division. A consideration of less importance, but nonetheless controversial, concerns the names that are to be applied to these higher taxa. As explained in the Scope and Format section of this catalogue [p. 7], the ICBN allows both descriptive and typified names for taxa above the rank of family. Although these names are exempt from the principle of priority (Art. 11.4), the ICBN recommends that priority be applied when choosing among typified names (Rec. 16B.1). We are thus allowed a latitude of choice sufficient to create a confusion of competitive schemes.
For reasons given in the Scope and Format section, class is the highest category used in this catalogue. When only one class of red algae is recognized (as in this catalogue), it is usually given the descriptive name Rhodophyceae, but if a typified name is preferred, Bangiophyceae has priority (see P. Silva, 1980b: 79). When two classes are recognized, one bears the name Bangiophyceae, with no alternative, while the other may bear either the descriptive name Florideophyceae or the typified name Nemaliophyceae (an elevation in rank of Nemaliophycidae Christensen, 1978: 66). When two subclasses are recognized within a single class of red algae to which the name Bangiophyceae is applied, one subclass bears the name Bangiophycidae (an autonym as specified by Art. 16.1) while the other subclass may bear either the descriptive name Florideophycidae or the typified name Nemaliophycidae. When two subclasses are recognized within a single class of red algae to which the name Rhodophyceae is applied (as in this catalogue), Bangiophycidae is not an autonym and is to be attributed to Engler (1892: 15, ``Unterklasse Bangiales'').
The two traditionally recognized groups of red algae seemed remarkably discrete at one time, but the distinction has been blurred by confirmation of pit connections in several non-floridean genera (Compsopogon, Rhodochaete, and the conchocelis-phase of Porphyraceae) and of other exceptionally shared characters. This blurring suggests that recognition of more than one class of red algae is unwarranted.
While agreeing that only one class of red algae should be recognized, Magne (1989) markedly altered the taxonomic value assigned to certain morphological characters and thus created a basis for the recognition of three subclasses. Placing greatest value on the nature of reproductive parent cells (``cystes''), Magne proposed the subclass Archaeorhodophycidae to encompass the Porphyridiales (in which specialized reproductive cells are unknown), the subclass Metarhodophycidae to encompass the Erythropeltidales, Rhodochaetales, and Compsopogonales (in which only part of the contents of a reproductive parent cell is transformed into a spore or gamete), and the subclass Eurhodophycidae to include the Bangiales as well as all floridean orders (in which all the contents of a reproductive parent cell is transformed into one or more spores or gametes). The family Phragmonemataceae, in which endospores are known, was given a questionable position in the Archaeorhodophycidae. While this classification expresses differences in a seemingly important phylogenetic character, I do not think that it is particularly useful beyond conveying that information. I believe that despite significant differences, there is sufficient common ground among the Archaeorhodophycidae, Metarhodophycidae, and Bangiales to warrant the traditional recognition of the Bangiophycidae in contrast with the Florideophycidae (Nemaliophycidae), at least for pedagogical purposes.