Gomphadelpha (Bacillariophyceae) – a new genus name for taxa formerly subsumed under the name Gomphoneis herculeanum-complex. Gomphadelpha (Bacillariophyceae)

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 discovered that the genus Gomphoneis was not monophyletic. Some taxa – such as Gomphoneis herculeanum var. minuta clustered molecularly next to taxa of the Gomphonema core group within the family Gomphonemataceae as expected. Other taxa, such as Gomphonella olivacea and G. tegelensis which have been shown to be morphologically close to the generitype 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 North Californian creek. The molecular data (rbcL and 18SV4) put this species within the taxa clustering next to the Gomphonema core group. Since the genus name Gomphoneis was tied to the G.elegans-group which clustered outside the Gomphonemataceae, this group of taxa received the new name Gomphadelpha based on the new taxon G. kociolekii. Besides molecular data, the new genus Gomphadelpha can be separated well also morphologically from Gomphoneis and Gomphonella in showing not only the typical Gomphonema outline but also areolae which are differentiated between the valve and the foot pole as well as a single round stigma which is slit-like internally in contrast to undifferentiated apical poles and no or several stigmoids. The autapomorphies to Gomphadelpha are clear with well visible longitudinal lines produced by the internal axial plate as well as differently formed volae covering the external areolae which sit in deep troughs.