Genus Alexandrium Halim emend. Balech, 1989
This genus has extensive synonymy due to continual scrutiny of toxic species causing public health economic, and ecological problems. Cells armoured. Cells typically spherical to hemispherical to oval to slightly biconical, but without horns or spines. Descending median cingulum without overhang or contortion, displaced 1-1.5 cingulum widths. Surface markings include pores and reticulae. Thecae can be thin and delicate to rugose. Cytoplasm includes elongate to C-shaped nucleus and all species contain chloroplasts. In some species the apical pore plate (Po) comes in direct contact with the 1' plate; in others the Po is displaced from or is indirectly in contact with the 1' plate via a thread-like suture (e.g. A. ostenfeldii). Po with foramen, a relatively large comma-shaped cavity (or sometimes fishhook shaped as in A. catenella and A. tamarense). It is a diagnostic feature of the apical pore complex (APC). Plate formula: Po, 4', 6'', 6c, 9-10s, 5''', 2''''.
Several species toxic. Toxic species can produce a number of neurotoxins that can lead to paralytic shellfish poisoning events.
Remarks: Species are differentiated by the following features: 1) shape and position of the Po plate; 2) shape and position of pores in the Po and sp plates; 3) size and shape of foramen; 4) shape of sa plate; 5) presence and size of the ventral pore; 6) displacement of 1 plate; 7) chain formation; 8) shape and size of 6 plate; 9) cell shape; and 10) cell dimensions.
Species included from this genus:
Alexandrium acatenella (Whedon et Kofoid) Balech, 1985b
Alexandrium catenella (Whedon et Kofoid) Balech, 1985b
Alexandrium minutum Halim, 1960
Alexandrium monilatum (Howell) Balech, 1995
Alexandrium ostenfeldii (Paulsen) Balech and Tangen, 1985
Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki and Fukuyo, 1992
Alexandrium tamarense (Lebour) Balech, 1985b
Alexandrium tamiyavanichi Balech, 1994