Two developments since I wrote my post on Batrachospermum (“Algae … cunningly disguised as frog spawn”): first, two of the images (my field view and Chris Carter’s microscopic shot) are going to appear in a book “Freshwater Life in South Africa” and, second, the genus Batrachospermum has been split into two. This presents a slight problem as I no longer have the field material and so cannot determine whether the images are of true Batrachospermum or of the new genus Sheathia. However, as the book is intended for a lay audience, the nuances of red algae taxonomy can be sidestepped and, in any case, the key ecological “message” in this case is mostly obtained by recognising the genus (or, as we should now say, genera).
The paper is Molecular and morphological evidence for Sheathia gen. nov. (Batrachospermales, Rhodophyta) and three new species by Eric Salomaki and colleagues and it can be found in the latest issue of the Journal of Phycology (volume 50, pages 526-542). It is a very neat study, collecting specimens of Batrachospermum from all over the world and subjecting these to molecular analyses. The outcome was a molecular “tree” that indicated quite clearly that one group of taxa within the genus was genetically quite distinct from the others. So far, so good, but do these genera have any characteristics other than just different DNA? The answer turns out to be that the main axis of cells in Batrachospermum is composed of cylindrical cells whilst that of Sheathia is a mixture of cylindrical and bulbous cells. Although red algal taxonomists already knew that there was a group of Batrachospermum species with this property, it was only when the morphological and molecular evidence was combined that there was a strong case for splitting these off into a new genus.
Seven species of Batrachospermum are listed in the Freshwater Algal Flora of the British Isles. Of these, three have now been transferred to Sheathia. As I said in my earlier post, genus level identification is usually adequate for the purposes of general ecological assessment, so most of our current records will not allow us to differentiate between these two genera. The ecological notes in the Flora are not particularly helpful but do suggest that there is quite a lot of overlap in the preferences of the various species, so I doubt whether this split will result in a change in the way we interpret data. On the other hand, as we re-organise our synapses to accommodate this change, maybe someone will have a flash of inspiration to prove me wrong.
Oh yes, and I will need to update my lecture notes too.