Pseudostaurosira borealis (Foged) M.L. García & al., 2017

Vijver, Bart Van de, 2023, Observations on the type material of Fragilaria construens [var. binodis] f. borealis Foged (Fragilariaceae, Bacillariophyta), Notulae Algarum 278, pp. 1-5 : 2-4

Pseudostaurosira borealis (Foged) M.L. García & al., 2017 ( Figs 1–21, 62–68)

Basionym: Fragilaria construens [ var. binodis ] f. borealis Foged, Bibliotheca Phycologica 15: 56, pl. III: fig. 6, 1974.

Homotypic synonym: Staurosira borealis (Foged) Witkowski & al. (in Witon & al. 2004)

Holotype: Foged sample 29/1954, C!

Type locality: outflow from a small lake near Thingvellir , Iceland, sample 29, coll. date 15.VII.1954, leg. N. Foged

Description: Frustules rectangular, connected to each other forming long, ribbon-like chains using marginal, spatulate interlocking spines ( Figs 62 & 63). Spines located on virgae at valve face/mantle junction ( Figs 64 & 65). Stipules absent. Valves rectangular in their middle part with often very weakly constricted valve margins, and clearly protracted, elongated rostrate to weakly subcapitate apices. Valve dimensions (n=50): length 11–20 µm, width 4–5 µm. Valve face flat, although very weak undulation occasionally observed ( Fig. 65, arrows). Sternum broad, linear to lanceolate. Central area lacking. Striae composed of 1–3 large rounded to squarish areolae and one areola on the valve mantle, 14–16 striae in 10 µm. Small volae arising mesh-like from the areolar opening, projecting inwards. Scattered pattern of very small siliceous papillae present around areolae ( Figs 64 & 66). Apical pore fields present on both apices, composed of at least 2 rows of relatively large, rounded pores. Mantle edge bearing dense row of siliceous mantle plaques ( Fig. 63). Girdle bands numerous, open, plain ( Figs 62 & 63), often with small fimbriate edge ( Fig. 63, arrow). Internally, virgae weakly raised with broad striae sunken between them ( Fig. 67). Areolae covered by internal, elliptical depositions. End wall thickened with a recessed apical pore field ( Fig. 68)

Most of the observed valves in the original material could be assigned to P. borealis ( Figs 1–21) or P. robusta ( Figs 42–55), the latter characterised by a typical deeply undulating valve outline. However, several populations showed either an intermediate valve outline between P. borealis and P. robusta ( Fig. 56–61) having an asymmetrically constricted, concave central part with one valve margin being more convex or straight. Most likely these valves should be considered to belong to P. robusta , but this is not straightforward for each of the illustrated valves. Van de Vijver & Kusber (2022) showed the original type population for P. robusta and also illustrated several valves with these intermediate features (see their figs 12–15). More problematic, however, are on one hand the observed groups of valves with clearly convex, often rounded margins ( Figs 22–30), smaller valve dimensions and a more cruciform valve outline ( Figs 31–37) and on the other hand narrower, more linear valves with weakly concave margins ( Figs 38–41). The first two groups show some resemblance with the 4 illustrated valves of P. pseudoconstruens in Witon & al. (2004, figs 18–21) and the two valves illustrated in Marciniak (1982, pl. I: figs 1, 2), belonging to the type of P. pseudoconstruens . As the original material of P. pseudoconstruens has not been properly investigated at present, it remains unclear whether these groups represent P. pseudoconstruens or whether the population now identified as P. borealis should be considered as being part of a highly variable P. pseudoconstruens , giving priority to the latter name as it is the oldest name in the species rank.

This research received support (Bart Van de Vijver) from the SYNTHESYS project (www.synthesys.info), financed by the H2020 Research Infrastructures Programme, to visit C. Dr Christian Lange and Prof. Dr Nina Lundholm, my hosts, are thanked for their help in the Foged collection. Dr Carlos E. Wetzel and Dr Agata Wojtal are thanked for their help with the original material from the Barbara Marciniak collection.

Foged, N. (1974). Freshwater diatoms in Iceland. Bibliotheca Phycologica 15: 1–118.

Garcia, M.L., Maidana, N.I., Ector, L. & Morales, E.A. (2017). Staurosira patagonica sp. nov., a new diatom (Bacillariophyta) from southern Argentina, with a discussion on the genus Staurosira Ehrenberg. Nova Hedwigia Beiheft 146: 103–123.

Krammer, K. & Lange-Bertalot, H. (2000). Bacillariophyceae, 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. pp. 1–578, Ergänzungen 579 –596, 167 pls (2188 figs). Heidelberg: Spektrum Akademischer Verlag.

Marciniak, B. (1982). Late glacial and Holocene new diatoms from a glacial lake Przedni Staw in the Piec Stawów Polskich Valley, Polish Tatra Mts. Acta Geologica, Academiae Scientiarum Hungariacae 25 (1– 2): 161–171.

Morales, E.A., Wetzel, C.E., Novais, M.H., Buczkó, K., Morais, M.M. & Ector, L. (2019). Morphological reconsideration of the araphid genus Pseudostaurosira (Bacillariophyceae), a revision of Gedaniella, Popovskayella and Serratifera, and a description of a new Nanofrustulum species. Plant Ecology and Evolution 152 (2): 262–284.

Van de Vijver, B. & Kusber, W.-H. (2022). Typification and transfer of Fragilaria undulata C.E.Cramer to the genus Pseudostaurosira (Staurosiraceae, Bacillariophyta) with some notes on the diatom species described by Carl E. Cramer. Notulae Algarum 225: 1–5.

Williams, D.M. & Round, F.E. (1988 '1987'). Revision of the genus Fragilaria. Diatom Research 2: 267–288.

Witon, E., Witkowski, A. & Lange-Bertalot, H. (2004). Hippodonta subcostulata (Hustedt) Lange-Bertalot, Metzeltin et Witkowski and some fragilarioid diatom taxa from the Holocene lacustrine sediments of the Faeroe Islands. Diatom Research 19 (1): 123–134.