Sellaphora blackfordensis D.G. Mann & S. Droop 2004

Introduction

Sellaphora blackfordensis was described formally by D.G. Mann & S. Droop in Mann et al. (2004), after having been referred to previously in several papers as phenodeme 3 (Mann 1984) or the 'rectangular' deme of the morphospecies S. pupula sensu lato (e.g. Mann 1999, Mann et al. 1999). Sellaphora blackfordensis is named after the small urban pool (Blackford Pond) in Edinburgh where it was first found. It seems to be common in the epipelon of muds that are rich in organic matter, in eutrophic lakes and ditches.

Characteristics

• Valves linear-elliptical, with broad, subcapitate poles (becoming rostrate in the smallest specimens); robust
• Dimensions: 19–57 µm × 8.0–9.75 µm (longest valves rarely seen in natural populations)
• Striae radiate, curved, with some intercalated short striae at the centre, 17.8–19.6–20.7 in 10 µm
• Areolae invisible in LM
• Axial area narrow
• Central area expanded (to c. 55–65% of the valve width), somewhat irregular, mostly bow-tie–shaped or transversely rectangular
• Raphe-sternum often well-defined in LM, through development of slight grooves alongside it externally
• Conopeum absent
• Raphe sinuous
• Central external raphe endings expanded, turned towards the primary side
• Terminal fissures doubly inflected, turned towards the secondary side
• Polar bars present, radiate or more rarely parallel
• Allogamous (mating system complex)

Type Data

DNA Barcode (cox1): GenBank EF164948.

Holotype:  specimen at England Finder S39/4 (bottom and right-hand edges of the finder co-located with the top and left-hand edges of the the specimen slide, when the label is to the left) on slide E16/4 "Blackford Pond, Dec. '83, mud (tissue)" in the herbarium of the Royal Botanic Garden Edinburgh (E). Holotype valve can be viewed on-line at http://rbg-web2.rbge.org.uk/algae/research/types/Sellaphora_blackfordensis_type.html

Similar Species

Many Sellaphora species have a linear-elliptical outline and broad subcapitate poles; Evans et al. (2007, 2008) and Mann et al. (2008) illustrate several species visually very similar to S. blackfordensis. Careful measurements of valve width and striation density can help to achieve a reasonably certain identification in LM, but for critical work confirmation should be made by DNA barcoding (Evans et al. 2007).

Ecology

Found so far only in the epipelon of eutrophic lakes, ponds and ditches. A preliminary ecological analysis of some British Sellaphora species has been carried out by Poulíčková et al. (2008)

Geographical Distribution

Distributional data are difficult to obtain, because the species is easily confused with other Sellaphora species. Barcode confirmations are available for several Scottish and English lakes.

References

Evans, K.M., Wortley, A.H. & Mann, D.G. (2007). An assessment of potential diatom “barcode” genes (cox1, rbcL, 18S and ITS rDNA) and their effectiveness in determining relationships in Sellaphora (Bacillariophyta). Protist 158: 349–364.

Evans, K.M., Wortley, A.H., Simpson, G.E., Chepurnov, V.A. & Mann, D.G. (2008). A molecular systematic approach to explore diversity within the Sellaphora pupula species complex (Bacillariophyta). Journal of Phycology 44: 215–231

Mann, D.G. (1984). Observations on copulation in Navicula pupula and Amphora ovalis in relation to the nature of diatom species. Annals of Botany, 54, 429-438.

Mann, D.G. (1988). The nature of diatom species: analysis of sympatric populations. In F.E. Round (ed.) Proceedings of the 9th International Diatom Symposium, 317-327. Biopress, Bristol and Koeltz Scientific Books, Koenigstein.

Mann, D.G. (1989). The species concept in diatoms: evidence for morphologically distinct, sympatric gamodemes in four epipelic species. Plant Systematics and Evolution, 164, 215 237.

Mann, D.G. (1989). The diatom genus Sellaphora: separation from Navicula. British Phycological Journal, 24, 1-20.

Mann, D.G. (1999). The species concept in diatoms (Phycological Reviews 18). Phycologia, 38: 437-495.

Mann, D.G., Chepurnov, V.A. & Droop, S.J.M. (1999). Sexuality, incompatibility, size variation, and preferential polyandry in natural populations and clones of Sellaphora pupula (Bacillariophyceae). Journal of Phycology, 35, 152-170.

Mann, D.G., McDonald, S.M., Bayer, M.M., Droop, S.J.M., Chepurnov, V.A., Loke, R.E., Ciobanu, A. & du Buf, J.M.H. (2004) Morphometric analysis, ultrastructure and mating data provide evidence for five new species of Sellaphora (Bacillariophyceae). Phycologia 43: 459-482.

Mann, D.G., Thomas, S.J. & Evans, K.M. (2008). Revision of the diatom genus Sellaphora: a first account of the larger species in the British Isles. Fottea 8: 15–78.

Poulíčková, A., Špačková, J., Kelly, M.G., Duchoslav, M. & Mann, D.G. (2008). Ecological variation within Sellaphora species complexes (Bacillariophyceae) – specialists or generalists? Hydrobiologia