Staurosirella informis (W. Sm.) Van de Vijver, 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 informis (W. Sm.) Van de Vijver comb. nov.

Fig. 3 , Supplementary material 4

Odontidium informe W. Sm. (basionym), Annals and Magazine of Natural History, second series 19: 10, plate II, fig. 12 a – c. 1857. ( Smith 1857)

Type locality.

Gave de Lizez, Cauterets, Pyrenees Mountains, France, Jul. 1856.

Lectotype.

BR- 4821 (designated here), slide made from Smith sample Gave de Lizez. Figure 2 N illustrates the lectotype.

Registration for the new combination.

http://phycobank.org/103339

Registration for the typification.

http://phycobank.org/103842

Analysed material.

FRANCE • Cauterets, Gave de Lizez ; William Smith sample Gave de Lizez, slide BR- 4821 ; BR • Gave de la Reine ; William Smith sample Gave de la Reine, slide BR- 4822 ; BR .

UNITED KINGDOM • Redesdale, Hermits Well ; Aug. 1856; leg. R. K. Greville; Walker Arnott sample S 445, slide BR- 4823 ; BR .

LM description.

Frustules rectangular in girdle view, solitary, but occasionally forming short band-like chains. Valves isopolar, rhombic-lanceolate in larger valves, becoming more strictly lanceolate in smaller specimens. Apices not protracted, cuneately to broadly rounded. Valve dimensions (n = 20): length 15–22 µm, width 7–9 µm. Sternum moderately broad, lanceolate, slightly widened near the centre. Striae not broader than the virgae, weakly radiate throughout the entire valve, 6–7 in 10 µm. Areolae occasionally weakly discernible in LM (e. g. Fig. 3 H – I ). Figure 3 B – R .

SEM description.

Sternum and vimines externally raised above the striae. Weakly raised parallel ridges present on the virgae. Single or double, irregularly shaped spines present on the virgae, with a large number of small granules present between the spines on virgae and vimines. Striae composed of linear, slit-like areolae, separated by thin vimines. Areolae diminishing in length near the sternum. Apical pore fields present on both apices, equal in size and shape, composed of at least 7 long rows of small, rounded pores, covered occasionally by small silica plates. Valvocopula very large, plain, with distinct fimbriae. Internal areola occlusions formed by finely branched volae. Figure 3 S – V .

Associated diatom flora.

The type population was found in a sample from the Gave de Lizez, a stream in the French Pyrenees (region de Bigorre, Haute-Pyrenées, France). The sample is dominated by Achnanthidium gracillimum (F. Meister) Lange-Bert. , A. trinode Ralfs , Brachysira neoexilis Lange-Bert. , Denticula tenuis , Fragilaria perdelicatissima Lange-Bert. & Van de Vijver , Staurosirella neopinnata , and Staurosira tabellaria (W. Sm.) Leud. - Fortm., together with several species of Cymbella , Delicata , and Gomphonema . According to Lange-Bertalot et al. (2017), this diatom community points to an alkaline, oligo- to weakly mesotrophic, carbonate-enriched substrate. The Walker Arnott population from Redesdale, a valley in the western part of Northumberland, (northeast England, United Kingdom) closely resembles this species composition, with high numbers of Brachysira neoexilis , Delicata delicatula (Kütz.) Krammer , Denticula tenuis , Eucocconeis flexella (Kütz.) F. Meister , and Fragilaria cf. amphicephaloides Lange-Bert. , indicating almost similar conditions, though the listed species thrive more in standing waterbodies such as larger lakes ( Lange-Bertalot et al. 2017).

Figures

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).

Figure 3. Staurosirella informis (W. Sm.) Van de Vijver comb. nov., LM and SEM micrographs taken from the original Smith material (BR- 4821, Cauterets, Gave de Lizez, France). A. Original drawing from Smith (1857: fig. 12). B – C. LM pictures of two frustules in girdle view. D – R. LM pictures of valves in valve face view in decreasing length. S. SEM external view of a complete valve. T. SEM external detail of the footpole showing the large apical pore field. U. SEM view of the valvocopula with the fimbriate extensions. V. SEM internal view of a complete valve. Scale bar = 10 µm (B – S, U – V), 1 µm (T).