Alexandrium ostenfeldii cells are generally considered to be larger, and longer than wide, while A. peruvianum cells appear smaller and slightly wider than long. The straight (or sometimes irregular) anterior and posterior right margins of the

narrow 1′ plate of A. ostenfeldii (Paulsen 1904) form a distinct angle around a large ventral pore, whereas in A. peruvianum the right anterior margin of this plate is typically curved, and the enclosed pore is smaller (Balech and de Mendiola 1977). The s.a. plate in A. ostenfeldii is generally low and wide with a horizontal anterior margin and a slightly oblique right end that makes it appear like a door-latch. In A. peruvianum, this plate is A-shaped or triangular. The 6″ plate is also typically wider in A. ostenfeldii compared to A. peruvianum. G. dimorpha was described from material collected in a coastal RAD001 in vitro Mediterranean lagoon of Southern France (Biecheler 1952) and appears distinct from the former two species by a conspicuously wide and anteriorly extended 1′ plate and a horseshoe-shaped s.a. plate that penetrates into the epitheca. Given that the identity of the latter species has not been accepted by some authors (Balech 1995), and examination of the type material was not possible, this species has never been formally transferred to the genus Alexandrium.

Although morphological differences FK506 chemical structure among A. ostenfeldii and A. peruvianum, were well defined in the material originally investigated, further studies on samples from other locations revealed that distinctive plate characters vary considerably

among and within geographic populations and even within strains (Balech 1995, MacKenzie et al. 1996, Cembella et al. 2000, Lim et al. 2005, Kremp et al. 2009). Given this extensive morphological variation, recent A. ostenfeldii and A. peruvianum identifications have been made with reservations, and scientists repeatedly emphasized the necessity 上海皓元 to re-assess the validity of distinctive characters (Lim et al. 2005, Kremp et al. 2009). Consistent assignment has furthermore been complicated by the lack of consensus regarding the weight of the different diagnostic features: while some investigators have given priority to the s.a. shape (Bravo et al. 2006, Tomas et al. 2012), others considered the anterior 1′ margin most important (MacKenzie et al. 1996, Kremp et al. 2009). In addition to these inconsistencies, morphogenetic identification is not simple either, despite the availability of extensive sequence data and recognition of specific genetic signatures (Touzet et al. 2011). GenBank contains numerous identical sequences from isolates assigned to A. ostenfeldii and A. peruvianum. The need for clear identification guidelines and a better taxonomic understanding of the A. ostenfeldii group is becoming more and more evident, since blooms of the respective species have increased significantly in the past decades. Both A. ostenfeldii and A.