Staurosirella crux (Ehrenb.) Van de Vijver & Kusber, 2024

Van de Vijver, Bart, Kusber, Wolf-Henning, Jüttner, Ingrid, Schuster, Tanja M. & Williams, David M., 2024, Revision of the Staurosirella leptostauron complex (Staurosiraceae, Bacillariophyta) in Europe with the description of three new species, Plant Ecology and Evolution 157 (2), pp. 174-201 : 174-201

Staurosirella crux (Ehrenb.) Van de Vijver & Kusber comb. nov.

Figs 1 , 2 , Supplementary materials 1, 2 A – J, 3 A – B

Navicula crux Ehrenb. (basionym), Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben der Natur: 184. 1838. ( Ehrenberg 1838)

Biblarium crux (Ehrenb.) Ehrenb. ( Ehrenberg 1845: 74)

Odontidium harrisonii W. Sm. ( Smith 1856: 18)

Dimeregramma harrisonii (W. Sm.) Ralfs ( Pritchard 1861: 790)

Fragilaria harrisonii (W. Sm.) Grunow ( Grunow 1862: 368)

Diatoma harrisonii (W. Sm.) Cleve ( Cleve 1868: 219)

Rhaphoneis harrisonii (W. Sm.) O’Meara ( O’Meara 1875: 296)

Staurosira harrisonii (W. Sm.) Grunow ( Cleve and Möller 1877: No. 25)

Nematoplata harrisonii (W. Sm.) Kuntze ( Kuntze 1898: 416)

Staurosirella lata Levkov et al. ( Levkov and Williams 2011: 5)

Staurosirella harrisonii (W. Sm.) E. Morales & C. E. Wetzel ( Morales et al. 2015: 468)

Type locality.

Germany, Polierschiefer bei Cassel, Ehrenberg BHUPM drawing sheet 2348, BHUPM sample 2726.

Lectotype.

BHUPM 420310 ε w ‘ Cassel’ (Kasten = case 42, Buch = folder 3, mica strip 10 ε white ring) (designated here), specimen illustrated as our Fig. 1 D .

Isolectotype.

BHUPM s. n., specimen illustrated as our Fig. 1 G (designated here).

Registration for the new combination.

http://phycobank.org/103338

Registration for the typification.

http://phycobank.org/103841

Analysed material.

GERMANY • Polierschiefer bei Cassel ; Ehrenberg sample 2726, Ehrenberg [icon!] drawing sheet 2348 ; BHUPM • Moosach near München; Grunow sample s. n., Moosach W 0164841 [filed as Staurosira harrisonii under Odonti [di] um harrisonii in the general collection], slide BR- 4819 ; W, BR • Moosach near München ; Kützing sample 921, slide BR- 4820 ; BR .

UNITED KINGDOM • Hull ; 15 Jan. 1854; Smith sample s. n., slide BR- 4685 ; BR .

LM description.

Frustules in girdle view rectangular, solitary. Valve outline cruciform in larger valves becoming subovoid / rhomboid in smaller specimens, usually showing a rather irregular valve outline. Larger valves subtly heteropolar with one apex slightly wider than the opposite one, becoming distinctly heteropolar in the lower end of the size range. Apices not protracted, broadly rounded. Central inflations broadly rounded with a broad base. Valve dimensions (n = 30): length 10–36 µm, width 7–24 µm. Sternum rather wide, linear to weakly lanceolate. Striae narrower than the virgae, alternating, radiate to weakly curved, 5–6 in 10 µm. Individual lineolae in the striae usually well discernible in LM. Figures 1 , 2 A – M .

SEM description.

Valve surface uneven. Virgae with clearly raised transapical ridge. Striae uniseriate, composed of long, apically elongated areolae (= lineolae). Vimines broader than the areolae, becoming shorter towards the sternum and on the valve mantle. Spines irregular, rudimentary, grouped as verrucae-like structures on the valve face / mantle junction, located on the virgae in pit-like, shallow depressions. Apical pore fields very large, present on both apices, with both pore fields almost equal in size. Pore fields composed of a large number of parallel rows of very small, double, slit-like pores. Internally, valve surface more or less flat, with broad virgae and depressed series of areolae. Volae on the striae bifurcate, emerging from the longer inner side of the vimines. Figure 2 N – Q .

Associated diatom flora.

The lectotype population was observed in a fossil sample (Polierschiefer = layered diatomaceous earth) collected in the surroundings of Cassel, a town in central Germany (Hesse, Germany). According to Ehrenberg (1854), the silver-grey material has a Tertiary origin and is composed of freshwater organisms. Although highly fragmented, it is possible to identify several species in the sample such as Planothidium joursacense (Hérib.) Lange-Bert. , Cavinula scutelloides (W. Sm.) Lange-Bert. , and several species of Pseudostaurosira and Navicula . This species composition indicates more alkaline, mesotrophic, β-mesosaprobic conditions ( Lange-Bertalot et al. 2017). The type population of O. harrisonii in Hull is almost a monoculture of S. harrisonii with nearly 100 % of the observed diatom flora belonging to this species. The Moosach populations, however, are more diverse and dominated by taxa such as Achnanthidium exile (Kütz.) Heib. , Cocconeis pseudothumensis E. Reichardt , Denticula kuetzingii Grunow , D. tenuis Kütz. , Ellerbeckia arenaria (Moore) Dorofeyuk & Kulikovskiy , Eunotia alkalibiontica Lange-Bert. , Grunowia tabellariae (Grunow) Rabenh. , Odontidium mesodon (Ehrenb.) Kütz. , Staurosirella neopinnata E. Morales et al. , S. leptostauron (Ehrenb.) D. M. Williams & Round , and various species of Delicata , Cymbella , and Gomphonema . This species composition is usually found in oligo- to mesotrophic, calcium-bicarbonate enriched, alkaline conditions ( Lange-Bertalot et al. 2017).

Figures

Figure 1. Staurosirella crux (Ehrenb.) Van de Vijver & Kusber comb. nov., LM micrographs taken from the original Ehrenberg sample 2726 (Polirschiefer bei Cassel, Germany). A. Original drawing 2348 from the Ehrenberg Collection (Berlin, Germany). B – E. LM pictures of valves in valve face view from the original mica conserved in BHUMP, Berlin, Germany. F – H. LM pictures of prepared unmounted Ehrenberg material. Scale bar = 10 µm.

Figure 2. Staurosirella crux (Ehrenb.) Van de Vijver & Kusber comb. nov., LM and SEM micrographs taken from the original Smith type material for Odontidium harrisonii (BR- 4685, Hull, United Kingdom). A. LM picture of a frustule in girdle view. B – M. LM pictures of valves in valve face view in decreasing length. N. SEM external view of a complete valve. O. SEM external detail of the footpole showing the large apical pore field. P. SEM external detail of part of the central area with the marginal spines, the large virgae and the vimines. Q. SEM internal view of a complete valve. Scale bar = 10 µm (A – N, Q), 1 µm (O – P).