Blue-green algae constitute a minefield for the hapless cataloguer. In a previous catalogue (P. Silva, Meñez, & Moe, 1987), dealing with Philippine benthic marine algae, I discussed three major sources of frustration: insufficiency of ecological and geographic data on herbarium specimens or in published records or both; the Gordian knot of cyanophycean classification; and the complications of later nomenclatural starting points. A cataloguer can cope, albeit resignedly, with insufficient or uncertain collecting data, the worst that can happen being the omission of qualifying taxa or the inclusion of nonqualifying taxa. In trying to present the records in a readily comprehensible taxonomic scheme, on the other hand, the cataloguer will inevitably fall into the abyss that separates Geitlerians from Drouetians. Geitler (1942), building on the monographs of Bornet & Flahault (1886--1888) and Gomont (1892), recognized more than 1200 species distributed among 4 orders, 22 families, and 140 genera. Drouet (1981), on the other hand, believing that individual species of blue-greens are highly variable both in morphology and physiology, recognized only 61 species distributed among 2 orders, 6 families, and 24 genera.
Of the 61 species recognized by Drouet, 45 are represented in the present catalogue, either by records under those names or by records under names considered synonyms by Drouet. As in the Philippine catalogue, I have entered these alleged synonyms independently, believing that this arrangement conveys information that would be obscured were a Drouetian scheme alone to be followed. When a record is published under a Drouetian name, the particular ecophene that is involved can be determined only by referring to the description, illustrations, and comments in the publication. Such analyses have not been undertaken for this catalogue. When blue-greens are to be compared among themselves within a particular flora or community, a Geitlerian classification is preferable to a Drouetian classification in that it underscores rather than obscures morphological differences. Whether these differences delimit ecophenes or independent species should be considered immaterial to the field biologist.
The choice of a taxonomic scheme to accommodate Drouetian species as well as
their alleged synonyms is not easy.
For the Philippine catalogue, I relied on
whose comprehensive treatment of freshwater forms, with
incidental mention of marine forms, served well.
Recently, a taxonomic scheme
covering the entire spectrum of Cyanophyceae and involving major restructuring
in certain portions of the spectrum has been proposed
(Anagnostidis & Komárek, 1985; 1988; 1990 and
Komárek & Anagnostidis, 1986; 1989).
monumental work involves a reassessment
of traditional gross morphological characters coupled with the introduction of ultrastructural, biochemical, physiological, and ecological characters. While this scheme may be expected to change continually to accommodate new data and new interpretations of old data, it is an excellent framework for the Indian Ocean records by virtue of its comprehensiveness, its incorporation of data from all lines of current research, its unifying point of view, and the accompanying discussion of taxonomic problems and decisions.
In the Philippine catalogue (P. Silva, Meñez, & Moe, 1987: 127), I avoided the complications of later nomenclatural starting points by accepting 1 May 1753 (the date of publication of Linnaeus's Species plantarum, ed. 1, legislated by Art. 13.5) as the nomenclatural starting point for all Cyanophyceae. This iconoclastic practice is continued in the present catalogue.
To some biologists, the difficulties presented to a cataloguer of Cyanophyceae would be resolved if these organisms were considered bacteria. Whether the blue-greens are more closely related to bacteria than to algae is a taxonomic opinion depending partly on the phylogenetic value that is accorded each character and partly on the definition of bacteria and algae. Because I accord primary phylogenetic significance to the process of oxygen-evolving photosynthesis, I prefer to treat blue-greens as algae. Setting aside considerations of phylogeny, the treatment of blue-greens as algae or as bacteria depends on the point of view, purposes, and methodology of a particular research program. When the blue-greens are experimental material isolated and grown by microbiological techniques, it may be appropriate to consider them bacteria. When, however, the object of the research is to determine the representation of blue-greens in a particular flora or the position of blue-greens in the structure of a particular community, macrobiological techniques traditionally applied to algae are called for. Whether the research deals with blue-green algae or with blue-green bacteria is immaterial since any new information that may result is grist for the same taxonomic mill.
Those workers who are intimidated by the flux in the taxonomy of blue-greens may be encouraged by Lambert, Steinke, & Naidoo (1989), who were commendably forthright in explaining why they chose to treat these organisms as algae and to classify them according to a Geitlerian rather than a Drouetian scheme. Castenholz (1993), who considered the blue-greens to be bacteria, reviewed species concepts in this group. He favored the so-called Stanier/Ripka system, which is based on a variety of characteristics in culture and thus not directly useful for the field biologist.