Gomphonella olivacea

Valves are clavate, with a broadly rounded headpole and a narrow footpole. The valve tapers more strongly toward the footpole than to the headpole. The raphe is filiform and lateral. The raphe terminates internally distantly from the apices. The axial area is narrow, straight, and expanded laterally to form a rectangular central area bordered by shortened striae at, or near, the margin. Stigma are absent. Striae are costate and individual areoale are not visible in the LM. Striae are biseriate and radiate. The apical pore fields appear (with DIC optics) more like condensed striae rather than differentiated apical pore fields.

In North America, it has been treated as a member of Gomphoneis, as Gomphoneis olivacea (Hornem.) P.Dawson ex R.Ross and P.A.Sims 1978. This website also treated it as Gomphoneis olivacea, until 2019. In Europe, it has been treated within Gomphonema, as Gomphonema olivaceum (Hornem.) Bréb. 1838 (Hofmann et al. 2013, Levkov et al. 2016).

The phylogenetic relationships of Gomphonella olivacea, Gomphoneis and Gomphonema species have been examined based on gene sequences (18sV4, rbcl) (Jahn et al. 2019). This work led to the recognition and resurrection of Gomphonella (Hornem.) Rabenh., as well as the transfer of a number of species to Gomphonella. Future work will likely lead to further clarification of relationships in this group of diatoms.

Note that in the North American flora we recognize a more narrow concept than that suggested by Krammer and Lange-Bertalot (1986, pl. 165). The specimens illustrated in figs. 4-6 are similar to those in North America. Figures 1-3 appear to be of another taxon.