Abstract
Background and aims – We examine the possibility of the independent evolution of the same features multiple times across the pennate diatom tree of life.
 Methods and key results – Features we have studied include symmetry, raphe number and amphoroid symmetry. Phylogenetic analysis, with both morphological and molecular data suggest in each of these cases that the features evolved from 5 to 6 times independently. We also look at the possibility of certain features having evolved once and diagnosing large genera of diatoms, suggestive of an adaptive radiation in genera such as Mastogloia, Diploneis and Stauroneis.
 Conclusion – Formal phylogenetic analyses and recognition of monophyletic groups allow for the recognition of homoplasious or homologous features.
Highlights
For some time we have advocated basing diatom taxa, and by extension, the discovery of a natural system of classification, on monophyly alone (Kociolek & Williams 2015, Williams & Kociolek 2010)
It is heartening to see that some who raised issues in opposition to this criterion (Mann 1997, Medlin 2010, 2016, Medlin & Kaczmarska 2004) have adopted this approach (Medlin 2018, Vanormelingen et al 2007, 2008). In both morphological and molecular studies there has been a tremendous amount of work characterizing monophyletic groups and placing them within a natural classification (Lundholm et al 2002a, 2002b)
We have focused on this aspect of inconsistency because it is best rectified by reconsideration of the morphological characters involved
Summary
Background and aims – We examine the possibility of the independent evolution of the same features multiple times across the pennate diatom tree of life. Methods and key results – Features we have studied include symmetry, raphe number and amphoroid symmetry. Phylogenetic analysis, with both morphological and molecular data suggest in each of these cases that the features evolved from 5 to 6 times independently. We look at the possibility of certain features having evolved once and diagnosing large genera of diatoms, suggestive of an adaptive radiation in genera such as Mastogloia, Diploneis and Stauroneis. Key words – Diatoms, homoplasy, phylogeny, characters, monophyly, molecular data, morphological data, species flocks
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