The Level 1 certification indicates knowledge of the characteristics of diatom genera from inland North America, based on

The Level 2 certification indicates knowledge of 1) variation in diatom morphology within a species, 2) morphological operational taxonomic units (mOTUs), and 3) basic concepts of diatom nomenclature. The certification is intended to indicate a practical base for using a voucher flora to identify inland diatoms of North America. The exam evaluates proficiency in distinguishing mOTUs, recognition of specimens that should not be included in a mOTU without further investigation, assignment of formal scientific names to mOTUs using, and application of basic rules of botanical nomenclature.

Both exams are offered online and may be scheduled by completing an interest form on the Stroud website. Exams may be administered in connection with a conference or workshop, such as the Society for Freshwater Science annual meeting or the North American Diatom Symposium. For more information, contact [email protected].


The SFS Taxonomic Certification Program was established to certify that trained and skilled people are providing aquatic identifications in North America. The Stroud Water Research Center currently administers the program for SFS. The program also helps promote undergraduate and graduate training of new taxonomic experts, training of taxonomic technicians through workshops, development of new manuals for identifying aquatic invertebrates and algae, and taxonomic excellence in other disciplines and other parts of the world.

The Diatom Taxonomic Certification Committee (Diatom TCC), led by Sylvia Lee, has worked to develop the Level 1 and Level 2 exams. The committee (Sylvia Lee, Melissa Vaccarino, David Burge, Julianne Heinlein, Mark Edlund, Jan Stevenson and Sarah Spaulding) met regularly over past years to develop details of certification. The Diatom TCC obtained feedback from the diatom community to help develop fair and reasonable exams that serve the needs of water professionals and the broader diatom research community. We thank everyone who provided comments and suggestions.


The exam includes composite light and electron micrograph images of diatom genera, based on this website ( The list of genera included in the exam and the exam format is available through the links on this page. A practice test is available to learn the style of the exam. The exam includes 60 questions and participants will have 120 minutes to complete the exam. Additional time may be requested for reasonable accommodations.

A passing score of 95% is required for certification. A score of 90% allows a practitioner to retake the exam at no additional fee. The Level 1 certificate of proficiency is valid for 5 years.

The fee is set at $100 ($75 for SFS members). Additional information about examination fees is available on the Stroud website.


There are three sections in the exam. In section one, composite images of 3-5 diatom specimens belonging to a morphological size series are placed on the left. The Diatom TCC considers each series to belong to a single mOTU (the specimens belong to a single species). You will be asked if the specimen on the right belongs to the size series on the left. Do not consider species or morphological concepts beyond those illustrated in the plate. For example, do not use taxonomic keys, voucher floras, publications, or your personal collections which may show different size ranges and morphological variation. All scale bars on the images are equal to 10 ┬Ám.

Section two shows 3-5 diatom specimens belonging to a morphological size series. Respond by entering the formal scientific name from Include the genus name, specific epithet, and if applicable, the interspecific name (e.g., variety, form). Scientific names must be spelled correctly, so it is strongly recommended to copy and paste the taxon name from Do not include the author or year of publication. There is no need to italicize the name. The exam administrator will resolve issues related to spelling. In most cases, incorrect spelling of taxonomic names will not be accepted.

Section three includes multiple choice questions, each with four options. Select a) the complete and correct scientific name, or b) the basionym. The information needed to answer these questions is available on

Questions that include images also include a link which, when selected, will display a higher resolution image in a new window. Return to the exam window to answer the question.

The exam includes 100 questions and participants will have 180 minutes (3 hours) to complete the questions. Additional time may be requested for reasonable accommodations.

A passing score of 95% is required for certification. Through March 2024, the exam may be retaken one time at no additional fee and no minimum score requirement on the first attempt. We encourage test takers to provide feedback and suggestions for improvement of the exam by completing a post-exam survey.

The fee is set at $350 ($250 for SFS members). Additional information about examination fees can be found on the Stroud website.