Hello,
The issue mentioned here is well known in then field. It has been addressed most recently in Dreher et al. Harmful Algae 103 (2021) 102005 using phylogenomics and not morphological characters.
This paper establishes that Aphanizomenon flos-aquae falls within the same genus as Dolichospermum, and that almost any of the establish specific epithets are not monophyletic, including D. lemmermannii.
Many nomenclature changes will be needed. A group of us is in midst of sequencing 100+ genomes selected to fill gaps in the ADA clade/genus.
It’s best to await such a comprehensive result so that subsequent taxonomic adjustments won’t be necessary. For the time being, it’s best for GTDB to avoid using any established species names, and just use the strain number of a reference genome.
Theo Dreher
theo.dreher@oregonstate.edu