Reproduction in Microalgae

Algae have traditionally been included in the group Cryptogamae ('hidden reproduction'), as opposed to Phanerogamae or Spermatophyta, the Seed Plants. Cryptogamae encompassed both macro- and microalgae, lichens, mosses, and ferns, and have also been referred to as 'Thallophyta', 'non-vascular plants', 'spore plants', seedless or flowerless plants, depending on the criteria used for classification. Microalgae have long been considered among the more primitive and less important organisms representing the plant-like characters of autotrophy and immobility. Reproduction in macroalgae was only observed in the 18th century, but the ability of microalgae to reproduce sexually was not demonstrated until the 19th century in microscopic green filamentous algae. In this chapter, we summarise up-to-date information on sexual reproduction in three major groups of microalgae, the diatoms, dinoflagellates and haptophytes, and discuss its relationship to biodiversity and ecological life cycle strategies. Microalgae obviously constitute the microscopic part of the 'plant-like' world, but they do not deserve being considered lower 'plants', as they exhibit a perplexing diversity of modalities of sexual reproduction (haplontic, haplo-diplontic, diplontic life cycles), compared to the 'higher plants' which appear strikingly uniform and rather limited in their life cycle options.