Thecal plate morphology, molecular phylogeny, and toxin analyses reveal two novel species of Alexandrium (Dinophyceae) and their potential for toxin production

•Two new Alexandrium species, A. limii and A. ogatae, were described.•Goniodomins (GDs) were detected in the strains of A. limii, A. ogatae, and A. taylorii, with GDA as the major variant, but PSTs and cycloimines were undetectable.•GD-producing Alexandrium species were reported, for the first time, in the Southeast Asian region.•GD production is likely a common trait for species of the molecularly-defined Gessnerium clade of Alexandrium.