A Preliminary Investigation of the Phylogenetic Relationships Among the Freshwater, Apical Pore Field-Bearing Cymbelloid and Gomphonemoid Diatoms (Bacillariophyceae)

Relationships among the apical pore jeld-bearing diatom genera Brebissonia, Cymbella, Gomphonema, Gomphoneis, Didymosphenia, Gomphocymbella, and Reimeria and their close ally Encyonema were evaluated using cladistics.These biraphid genera are a polythetic group dejned by chloroplast number and type, mode of sexual reproduction, valve orientation and presence of apical porejelds.Character states of valve as well as non-siliceous features were described and then polarized using the outgroup method, with the naviculoid genera Anomoeoneis and Placoneis sewing as outgroups.The cladistic analysis suggests two groups of terminal taxa, corresponding to to a predominantly cymbelloid lineage and a goniphonemoid lineage.Didyrnosphenia, previously thought to be closely allied to gomphonemoid diatoms, is shown to be more closely related to Cymbella.Gom- phonema appears to be without distinguishing characteristics.Relationships of the other genera are described.The systematic position of small, doubly-punctate Gomphonema species is discussed.