Gomphadelpha (Bacillariophyceae) - a new genus name for taxa formerly subsumed in the Gomphoneis herculeana-group

Within the project German Barcode of Life - Diatoms diatoms of German waters were isolated and cultivated for integrative taxonomical research. In one of these studies, it was discov-ered that the genus Gomphoneis was not monophyletic. In terms of their molecular data some taxa - such as Gomphoneis herculeana var. minuta - clustered next to taxa of the Gomphonema core group within the family Gomphonemataceae as expected. Other taxa, such as Gomphonella oliva-cea and G. tegelensis, which have been shown to be morphologically close to the generitype of Gomphoneis - G. elegans - clustered outside this family but within the order Cymbellales. Since G. herculeanum had been described from North American waters by Ehrenberg 1845, its original material was studied in detail morphometrically and with high-resolution SEM. It was compared to strains and populations of a gomphonemoid taxon isolated from a mountain creek in northern Cali-fornia. The molecular data (rbcL and 18SV4) place this species within the taxa clustering next to the Gomphonema core group. Since the genus name Gomphoneis was tied to the G. elegans-group that clustered outside the Gomphonemataceae, we separated this group of taxa into a new genus described herein, Gomphadelpha, based on the new taxon G. kociolekii. Besides molecular data, Gomphadelpha can be separated morphologically from Gomphoneis and Gomphonella by having areolae that are differentiated between the valve and the footpole as well as a single round stigma that is slit-like internally, in contrast to undifferentiated apical poles and no or several stigmoids. In addition, the longitudinal lines are produced by the mantle lamella in Gomphoneis, in contrast to longitudinal lines produced mainly by the axial plate in Gomphadelpha. The autapomorphies to Gomphonema are clear with well visible longitudinal lines produced by the internal axial plate as well as differently formed perforations covering the external areolae which sit in deep troughs.

Automated summary

The German Barcode of Life - Diatoms project isolated and cultivated diatoms from German waters for taxonomic research. It was found that the genus Gomphoneis was not monophyletic, with some taxa clustering with the Gomphonema core group and others clustering outside the Gomphonemataceae but within the order Cymbellales. A new genus, Gomphadelpha, was described based on molecular and morphological data, and was differentiated from Gomphoneis and Gomphonella by certain characteristics.