Diversity: overview
Five morphological groups
Variation in valve shape and pattern can be used to
construct five groups of Sellaphora
species. Four of the five correspond quite closely to species
recognized in traditional classifications, e.g. by Hustedt (1930,
1927–66) and Krammer & Lange-Bertalot (1986), and
most records
of 'Navicula americana',
'Navicula laevissima'
(also known as N.bacilliformis),
'Navicula bacillum'
and 'Navicula pupula'
would refer to the equivalent group here. All of these traditional
'species' are in fact heterogeneous and they are not
necessarily monophyletic (although the 'laevissima' and
'bacillum' groups probably are).
However, even though some of the five groups may be
artificial, they are
convenient for explaining the range of form present in the genus and
for identification. The characteristics of each group are
given
below. Or, to
go directly to the group page, click on
the relevant image.
Key
- 'americana group': no polar
bars; wide axial area;
generally a rounded central area; linear or linear-elliptical outline
- 'laevissima group': no polar bars; narrow axial area;
rectangular or
rounded
central area; linear outline
- 'pupula group': with polar bars
(arrow); narrow axial area;
bow-tie-shaped, rectangular, diamond-shaped or irregular central area; outline variable, rarely simply
linear-elliptical or elliptical
- 'bacillum group': with polar bars
(arrow); narrow axial area;
rounded central area; linear or linear-elliptical outline
- 'seminulum group': no polar bars;
narrow axial area; variable central area; variable outline; small-celled
- incertae
sedis: some species currently assigned to Sellaphora cannot
be shoe-horned into any of the above categories and may
not even belong to the genus; these will be dealt with on a separate
page, once we have assessed all the relevant species
References
Hustedt, F. (1930). Bacillariophyta. In Pascher, A. [Ed.] Die
Süsswasser-Flora Mitteleuropas, vol. 10 (ed. 2). G. Fischer,
Jena.
Hustedt, F. (1927–1966). Die Kieselalgen
Deutschlands,
Österreichs und der Schweiz unter Berücksichtigung
der übrigen Länder Europas sowie der angrenzenden
Meeresgebiete. In Dr L. Rabenhorsts Kryptogamenflora von Deutschland,
Österreich und der Schweiz, vol. 7(3). Akademische
Verlagsgesellschaft, Leipzig.
Krammer, K. & Lange-Bertalot, H. (1986).
Bacillariophyceae 1.
Teil: Naviculaceae. In H. Ettl, Gerloff, J., Heynig, H. &
Mollenhauer, D. [Eds.] Süsswasserflora von Mitteleuropa, vol.
2/1. G. Fischer, Stuttgart & New York.
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