Observations on some species of the diatom genus Gomphonema C. A. Agardh

Gomphonema acuminatum var. coronatum Ehrenb., G. capitatum Ehrenb., G. constrictum Ehrenb., G. gracile Ehrenb., G. intricatum var. vibrio Ehrenb., G. subclavatum Grun. and G. ventricosum Greg. all conform to the basic features of the genus Gomphonema C. Ag. as exemplified by detailed electron microscopical studies of G. parvulum Kütz. This biraphidaceous diatom genus is characterised by heteropolar, asymmetrical cells which have a single isolated punctum, displaced somewhat from the centre of the valve. Electron microscopical observations reveal a reniform or horseshoe-shaped poroidal structure to the valve. It is suggested that this is found only in “true” members of the genus Gomphonema. Other “gomphonemoid” types with differing pore structure should be removed into related genera.