My earliest memories of being taught about biological classification – the best part of half a century ago – were of a binary split between “plants” and “animals”, with fungi occupying an anomalous position as plants that were unable to photosynthesise. Algae were the simplest plants and protozoans were the simplest animals. And that was that.
That might have been how biological classification was taught in a 1970s comprehensive school, but it was never quite that simple. You can get a flavour of the development of the ideas of how different groups of organisms were arranged by following this link. It reads like a synopsis of Game of Thrones but you’ll get the general idea: the two kingdoms that I learned about at school splinter into six (or seven, or eight, depending on who is writing) kingdoms by the dawn of the 21st century. Insights from molecular biology have been influential, but mostly for testing ideas developed by earlier generations of biologists rather than, necessarily, for paradigm-busting.
During the course of this, the idea of algae as the “simplest plants” has been blown apart. A crude geopolitical analogy is that “algae” were roughly equivalent to the old Yugoslavia, seemingly a coherent entity until the political upheavals at the end of the 1980s which precipitated its splintering into seven separate republics. The idea of algae, as a meaningful grouping, died, though the idea of a phycologist, as someone who studies algae, has persisted (see “Identity crisis?”).
The Seven Kingdom approach is summarised below, with the four groups containing algae indicated by arrows. The rest of this post will link these Kingdoms to the overviews of the major groups of algae that I have been writing. These, in turn, link to other posts which describe each of these groups in more detail.
First, in the Prokaryota Domain, we have the Cyanobacteria (see “Shuffling the pack …”). Meanwhile, in the Eukaryota, we have the Euglenophyta as the sole algal representative in the Protozoa (seen most recently in “Invisible worlds at Malham Tarn”), followed by the Chromista, which contains a large number of significant algal groups (see “Unlikely bedfellows …”). Finally, there are the Plantae which, alongside all the higher plants, contains the green algae (see: “The big pictures …”) and the red algae (see: “Rhapsody in red …”).
The Cyanobacteria evolved first, early in the Precambrian (see “As old as the hills …”) and all other algal groups are the result of a cyanobacteria-like cell being engulfed by another bacteria to become the chloroplast within a primitive eukaryotic cell. That first “endosymbiosis” gave rise to the red and green algae lines. The Euglenophyta evolved through a second endosymbiosis in which a protozoan engulfed a primitive green alga whilst the Chromista arose from a further endosymbiosis involving an ancient protozoan engulfing a primitive red alga. All Chromists arose through this endosymbiosis, although many (including the organisms responsible for potato blight and malaria) subsequently lost their ability to photosynthesise. All of these endosymbioses also probably took place in the Precambrian (fossil evidence is weak, in the case of the Chromista).
It seems to be obligatory now for all superhero franchises to include an “origin story” and, in terms of the evolution of life on earth, there are no organisms more deserving of the term “superhero” than algae. Without them, none of us would be here. Although, for someone with Irish ancestry, it is somewhat galling to have learned that potato blight, which drove my ancestors away, is caused by a rogue alga. Were it not for the Chromista, I might still be a member of the EU …
References
Cavalier-Smith, T. (2018). Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences. Protoplasma 255: 297-357.
Leilaert, F., Smith, D.R., Moreau, H., Herron, M.D., Verbruggen, H., Delwiche, C.F. & De Clerck, O. (2012). Phylogeny and molecular evolution of the green algae. Critical Reviews in Plant Sciences 31: 1-46. https://doi.org/10.1080/07352689.2011.615705
O’Neill, E.C., Trick, M., Henrissat, B. & Field, R.A. (2015). Euglena in time: evolution, control of central metabolic processes and multi-domain proteins in carbohydrate and natural product biochemistry. Perspectives in Science 6: 84-93. https://doi.org/10.1016/j.pisc.2015.07.002
Ruggiero, M.A., Gordon, D.P., Orrell, T.M., Bailly, N., Bourgoin, T., Brusca, R.T., Cavalier-Smith, T., Guiry, M.G., Kirk, P.M. (2015). A higher level classification of all living organisms. PLOSone DOI:10.1371/journal.pone.0119248
Stiller, J.W. & Hall, B.D. (1997). The origins of red algae: implications for plastid evolution. Proceedings of the National Academy of Science 94: 4520-4525
Some other highlights from this week:
Wrote this whilst listening to: lots of soul and Motown (see below)
Currently reading: Chronicles from the Happiest People on Earth by Wole Soyinka.
Cultural highlight: Summer of Soul, 2021 documentary film about the 1969 Harlem Cultural Festival, with footage of Stevie Wonder, the Staple Singers, Nina Simone, Gladys Knight and the Pips, B.B. King and many more. Uplifting.
Culinary highlight: Family meal at the Cook House, Ouseburn, Newcastle
microscopesandmonsters 