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Sellaphora Mereschkowsky 1902

David G. Mann
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Sellaphora living cellSellaphora valve
taxon links [up-->]Sellaphora blackfordensis [up-->]Sellaphora capitata [down<--]Sellaphoraceae Interpreting the tree
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The root of the current tree connects the organisms featured in this tree to their containing group and the rest of the Tree of Life. The basal branching point in the tree represents the ancestor of the other groups in the tree. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes and terminal taxa to the right.

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Note: this tree is still under construction. It does not yet contain all known Sellaphora subgroups.

Many further Sellaphora species exist (both described and undescribed) but have not yet been added to the tree
Containing group: Sellaphoraceae


Species of Sellaphora have been known since c. 1840 but were classified in the genus Navicula for most of time up to 1990. During most of the 19th and 20th centuries, diatom taxonomy was based almost entirely on the structure of the frustule (the silicified cell wall of diatoms); other features, such as chloroplast morphology, reproductive characteristics or nuclear behaviour, were not considered. There is nothing particularly unusual about the structure of the frustule in Sellaphora and so the original classification of Sellaphora species in Navicula (then a catch-all for undistinguished boat-shaped diatoms) is understandable. However, if chloroplast morphology is taken into account, differences between Sellaphora and Navicula species are immediately apparent. This was first noticed by Mereschkowsky (1902), who gave the following description:

‘Valve small, symmetrical, linear to elliptical, with obtuse ends, terminal nodules distant; striae usually fine, connecting-zone simple. Endochrome composed of one plate, resting with its narrow median part on the surface of one of the valves, with four long prolongations along the connecting zones. Pyrenoid absent. A few elaeoplasts, sometimes represented by two libroplasts.’

The key feature was the shape of the chloroplast (Mereschkowsky’s ‘endochrome’), which is a single H-shaped plate; this is what gives the genus its name (Sellaphora = ‘saddle-bearer’). Most 20th century floras reverted to the 19th century practice of including Sellaphora in Navicula and the species now assigned to Sellaphora (see below) were not always put in the same group within Navicula. However, following SEM studies of the frustule and new observations of the living cell and sexual reproduction, Sellaphora was reinstated as a separate genus (Mann 1989, Round et al. 1990). Molecular genetic data have thus far supported the monophyly of Sellaphora.

The history and taxonomy of Sellaphora are discussed by Mann (1989), Mann et al. (2008) and Evans et al. (2008). The genus has been developed as a model system for studying and documenting speciation in freshwater diatoms, including DNA barcoding (Evans et al. 2007). More is known about the mating systems of Sellaphora species than in any other diatom genus (e.g. Mann 1999, Mann et al. 1999).



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. (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., 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.

Mereschkowsky, C. (1902). On Sellaphora, a new genus of diatoms. Annals and Magazine of Natural History, series 7, 9: 185–195.

Round, F.E., Crawford, R.M. & Mann, D.G. (1990). The diatoms. Biology and morphology of the genera. Cambridge University Press, Cambridge, 747 pp.

Title Illustrations
Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new window
Sellaphora living cell
Scientific Name Sellaphora 'urban elliptical' deme
Specimen Condition Live Specimen
Identified By David G. Mann
Life Cycle Stage vegetative phase
Body Part single cell, focus series
View valve view
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2008 David G. Mann
Sellaphora valve
Scientific Name Sellaphora
Creator Frieda Christie
Acknowledgements This micrograph was taken by Frieda Christie, Royal Botanic Garden Edinburgh
Specimen Condition Dead Specimen
Identified By David G. Mann
Life Cycle Stage Vegetative phase
Body Part valve
View exterior, SEM
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2008 David G. Mann
About This Page

This page is being developed as part of the Tree of Life Web Project Protist Diversity Workshop, co-sponsored by the Canadian Institute for Advanced Research (CIFAR) program in Integrated Microbial Biodiversity and the Tula Foundation.

David G. Mann
Royal Botanic Garden Edinburgh, United Kingdom

Correspondence regarding this page should be directed to David G. Mann at

Page: Tree of Life Sellaphora Mereschkowsky 1902. Authored by David G. Mann. The TEXT of this page is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Mann, David G. 2010. Sellaphora Mereschkowsky 1902. Version 07 February 2010 (under construction). http://tolweb.org/Sellaphora/125733/2010.02.07 in The Tree of Life Web Project, http://tolweb.org/

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