ABSTRACT
Algae are an ancient and extremely diverse group of plantlike organisms, with representatives of the blue-green algae (cyanobacteria) being present for the last 3550 million years (Schopf and Walter, 1982). They range in morphology and size from microscopic picoplanktonic cyanobacteria (<2 µm in diameter) which are prokaryotic and closely resemble other eubacteria, a variety of unicellular, multicellular, filamentous and thalloid forms, to giant kelps that may be up to 60 m long. Their taxonomy is problematic, but it is clear on the basis of both traditional taxonomy and modern molecular techniques that they are polyphyletic (Bold and Wynn, 1985; Cavalier-Smith, 1993). The ‘amount’ of algal biodiversity, as in other groups of organisms, is largely unknown, however, the advent of molecular biological techniques and improvements in electron microscopy have greatly increased our knowledge-base and assisted in elucidating inter-relationships. Approximately 37 000 species of algae have been recognized/described (Table 8.1) but estimates of the total number of algal species vary from a relatively conservative 40 000 to >10 000 000 (Hawksworth and Mound, 1991; John, 1994).
