Algal perspectives: The algal phyla

What are algae? United States Supreme Court Justice Potter Stewart said of pornography, “I shall not today attempt further to define [it]… but I know it when I see it” (Jacobellis v. Ohio, 1964). Something similar could be said of algae. They are not one kind of thing but are a diverse assemblage of (mostly) oxygenic phototrophs, excluding embryophytes (which wags call the “drier algae”). The term is a form classification, not a phylogenetic one, and yet can be useful. There are commonalities of gross appearance, habitat, ecological role, and economic import or potential. Nonetheless, it can be a challenge to understand the full diversity of organisms within our purview as phycologists (algologists), and there are far more algae to know than there are scientists studying them (Figure 1). In his 2012 and 2024 Perspectives, Guiry identified 14 phyla and 63 classes of algae and noted that ongoing discovery continues to expand the list (Guiry, 2012, 2024). The 2012 article has received 8151 full-text views and 696 citations, and the 2024 update has already had 5586 full-text views. This high level of engagement illustrates the hunger for accurate, authoritative, and digestible fundamental information about these organisms. To respond to that interest, I am working with the Journal of Phycology to launch a new series of Perspectives. Each will consist of a short synopsis of a single phylum or class by a leading scholar. They will be intended to be accessible to a broad scientific audience but still be interesting to experts. Of course, these articles will have to be as diverse as the lineages that they are describing, and we anticipate that over time the scope of the series will grow and change. It is our hope that when compiled, these Perspectives will serve as an introduction to the current state of knowledge of algae and provide inspiration for the work that lies ahead. CFD envisioned and wrote the manuscript, took all of the photographs and micrographs in the figure, and prepared the figure and caption.