What is aquatic botany?— And why algae are plants: The importance of non-taxonomic terms for groups of organisms

• In a changing world, a general term is needed for photosynthetic organisms.
• The importance of Non-Taxonomic terms for Groups of Organisms (NTGOs) is discussed.
• Plants are defined as those organisms which carry out chloroxygenic photosynthesis.
• Algae are defined as all plants excluding the Embryophyta.

There are many Non-Taxonomic terms for Groups of Organisms (NTGOs) used in aquatic biology, without which it would not be possible to describe biotas and ecosystems. It frequently causes confusion when authors and readers assume different meanings of the same term, and NTGOs should be defined wherever appropriate.I here propose a broad definition of the NTGO ‘plants’, and an argument for the usefulness of the NTGO ‘algae’ as a sub-set of plants. The acceptance by some of ‘plants’ as a term precisely equivalent to either the Kingdom Plantae or the Superphylum Embryophyta is, in my opinion, unnecessary, contrary to custom, contrived, and of very limited usefulness.As we are facing our greatest ever challenge in global climate change, and the key process in this is photosynthesis, we need a simple term in English for chloroxygenic autotrophs. The only word likely to be generally acceptable is ‘plants’.I thus propose that plants are defined as those organisms which carry out chloroxygenic photosynthesis. This includes the Embryophyta, many groups of photosynthetic eukaryotic algae in different branches of the Tree of Life, as well as Cyanobacteria. Algae are similarly, and simply, defined as all plants excluding the Embryophyta.This is not intended to preclude organisations and publishers which use ‘botany’, ‘plants’ or ‘algae/phycology’ in their name from including whichever organisms they wish in the ambit of their deliberations or publications, provided the scope is logical and clearly specified.