Germainiella emmae (Van de Vijver & Cox) Kociolek, You, R.Lowe & Q.Wang, 2019

Kociolek, J. P., You, Q. M., Lou, F., P. Yu, Lowe, R. L. & Wang, Q. X., 2019, First Report and New Freshwater Species of Germainiella (Bacillariophyta) from the Maolan Nature Reserve, Guizhou Province, China, Phytotaxa 393 (1), pp. 35-46 : 43

Germainiella emmae (Van de Vijver & Cox) Kociolek, You, R.Lowe & Q.Wang , comb. nov.

Basionym: Fallacia emmae Van de Vijver & Cox 2015 , Cryptogamie, Algologie 36:247.

Several authors ( Metzeltin et al. 2005; Van de Vijver & Cox 2015) have commented on their perception of a close phylogenetic relationship between Germainiella and Fallacia , but morphological evidence in support of that conclusion of relatedness seems scant. Both Germainiella and Fallacia have conopea, but so do other diatoms within or near the Sellaphoraceae , including Sellaphora ( Round et al. 1990) , Microcostatus ( Johansen & Sray 1998: 97–98) among others, and the structure of the conopeum in Germainiella and Fallacia sensu stricto seems quite different from one another.

The conopeum has been described for a wide range of taxa: Nitzschia dissipata (Kützing) Rabenhorst (1860: 948) and relatives (e.g. Liu et al. 2015), Sellaphora ( Round et al. 1990) , Microcostatus ( Johansen & Sray 1998) , Fallacia ( Sabbe et al. 1999; Li & Nagumo 2014), and Pseudofallacia ( Liu et al. 2012: 624) . Lange-Bertalot et al. (1990) distinguished between siliceous coverings that originated from the axial area (conopea) versus the margin (pseudoconopea). The extent of a conopeum may be great to absent within a genus, and even within a single species. Metzeltin et al. (2005, plate 46, fig. 3) illustrate the entire valve face being covered (except for two narrow grooves, one on either side of the axial area) in Microcostatus werumii Metzeltin et al. (2009: 59) . Given the phylogenetic distance between the Bacillariales and Sellaphorales within the raphid diatom tree of life ( Sims et al. 2006), it seems likely that the conopea of these two groups are not homologous. And just as there is now some momentum to re-evaluate the naming of structures such as “stigmata”, whose structure is quite different between taxa and must also not be homologous (compare the phylogenetic position of Luticola species with members of the Cymbellales , both of which are described as having ‘stigmata’). The phylogenetic separation between Bacillariales and Sellaphorales may be as great as or greater than between Luticola and Cymbella , suggesting a review of the terms “conopeum” and how it is applied may be warranted.

Fallacia and Germainiella , also share the presence of internal hymenate occlusions. That feature, however, seems to help diagnose an entire family or order of raphid diatoms (Davidovich et al. 2015; Kulikovskiy et al. 2018). Synapomorphies suggesting a close relationship between Fallacia and Germainiella seem to be wanting.

A summary of the taxa in Germainiella suggests it is composed of the following eight taxa: G. engimaticoides Lange-Bertalot & Metzeltin in Metzeltin et al. 2005

G. enigmatica (Germain) Lange-Bertalot & Metzeltin in Metzeltin et al. 2005

G. clandestina Le Cohu, Ten-Hage et BartheÌs 2016

G. legionensis Borrego-Ramos et al., 2018: 184–185

G. emmae (Van de Vijver & Cox) Kociolek et al. , comb. nov.

G. sinica Kociolek et al. , sp. nov.

G. maolaniana Kociolek et al. , sp. nov.

G. guizhouiana Kociolek et al. , sp. nov.

The genus is cosmopolitan, being known from Europe, South America, Africa and Asia.

Other taxa worth exploring as possible members of the genus Germainiella include species with areolae that are difficult or impossible to discern with light microscopy from the Navicula minusculae Cleve group, from which several genera have been recently segregated (e.g. Microcostatus , Humidophila, Chamaepinnularia Lange-Bertalot & K.Krammer in Lange-Bertalot & Metzeltin (1996: 32) and others). Taxa such as N. pseudoexilissima Hustedt (1948: 46) , N. iranensis Hustedt (1962: 262) , N. mollissima Hustedt (1962: 263) and others in this group, as well as from the section Naviculae subtillissimae Hustedt (such as Navicula perlucida Hustedt 1937: 250 ) should be studied to determine if they also belong in Germainiella . Finally, the taxonomic and systematic position of species assigned to Fallacia but lacking the diagnostic features of the genus as typified by F. pygmaea , such as F. subhamulata , might be re-evaluated and perhaps better placed in Germainiella , or a new, separate genus.