Diatom taxonomy

High quality and detailed taxonomy is a prerequisite in the formation of reliable training sets. This becomes even more important when multiple analysts enumerate samples that will later be merged together. Within the MOLTEN and DEFINE projects the five diatom analysts work closely together and use slide exchanges, cross counting exercises and this web site as forums to further taxonomic harmonisation.

One of the original tools to be developed from these projects were the publicly available transfer functions to reconstruct nutrient histories based on counts that other diatom analysts might have made. For certain groups of taxa the demarcation of individual species is difficult, and accordingly, individual ideas of the species concept for taxa can vary widely. Such inconsistencies can affect the reliability of the results of transfer functions. In an attempt to mitigate such affects, a decision was taken to create aggregates for difficult species groups, where borders between species might be blurred and vary between the different analysts. The merges to create the aggregates are performed by a relational database, leaving each analyst free to enumerate samples at the taxonomic level they are comfortable with, but ensuring all samples are harmonised according to the agreed taxonomy. Formatting of other people’s count data to be in accordance with the MOLTEN and DEFINE taxonomic protocols is made available within the transfer function tool.

The aggregates (which all include at least two different species) are shown in the table below. It should be stressed that inclusion of a species in an aggregate does not indicate that the analysts disagree with the definition or validity of that species, the use of aggregates is purely practical.

There are other instances where varieties are not distinguished from each other, and all are reported under the nominate name, these instances are given here:

• Cocconeis placentula includes C. placentula, C. Placentula v. euglypta, C. placentula v. lineata and C. Placentula v. pseudolineata
• Denticula tenuis includes D. tenuis and D. tenuis v. crassula
• Dimeregramma minor includes D. minor and D. minor v. nanum
• Diploneis smithii includes D. smithii and D. smithii v. rhombica
• Fragilaria capucina includes F. capucina, F. capucina v. gracilis and F. capucina v. mesolepta
• Gomphonema olivaceum includes G. olivaceum and G. olivaceum v. salinarum
• Melosira lineata includes M. lineata, M. lineata v. juergensii and M. lineata v. orichalcea
• Pseudostaurosira brevistriata includes P. brevistriata and P. brevistriata v. inflata

A final word on the pictures from this website, more are indeed on their way to being made publicly available. In the meantime the references we give to floras can be used as a guide to the species concepts adopted by these projects.

Genera browse

This page lists all genera which have species with a maximum abundance >1% and found in more than one site.
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Click on a name to view a list of species found.