Diatoms in the Herbarium

The diatom, Lyrella sp., photo from Fish and Wildlife Research Institute

The diatom, Lyrella sp., photo from Fish and Wildlife Research Institute

Diatoms are microscopic aquatic organisms that have glass-like shells.  These structures are symmetrical, and this symmetry combined with the transparency of the “glass” and the variety in their shapes makes them aesthetically awesome.  Their diversity and ubiquity in both fresh and saltwater environments also make them very important ecologically.  A few months ago, I visited the Diatom Herbarium at the Academy of Natural Sciences in Philadelphia, now part of Drexel University. Maria Potapova, the assistant curator in charge of the herbarium, gave me a tour and showed me some of the hundreds of thousands of specimens in the collection.  The usual metal herbarium cabinets are filled with box after box of glass microscope slides. In addition, there are vials and small bottles containing with the sandy remains of diatoms. Potapova explained why it is such a slow process to digitize the information about the specimens. A single vial may hold a number of diatom species, and individual species from these vials may have been mounted on a number of different slides. However, the links between slides and vials may not have been noted. Making these connections is possible through dates, collectors, etc., but it takes time.

Potapova also showed me several rare exsiccatae that contain many type specimens. The oldest, that of the German botanist Friedrich Traugott Kützing—Algarum Aquae Dulcis Germanicarum (1833-1836)—is in 16 notebooks with specimens wrapped in tiny paper envelopes or on glass. Another is the set of 22 small leather-bound book-like boxes filled with slides. The title on each spine is Diatomées de Belgique (1882-1885), and the collection was assembled by the Belgian botanist Henri Van Heurck. These are among the treasures of the collection, which includes specimens gathered in the 1800s by members of the ANS, many of whom were wealthy men who had microscopy as a hobby. The origins of the collection was in the Microscopical Society of Philadelphia, founded 1858. The first evidence of interest in diatoms at the ANS were three papers on marine and freshwater diatoms published by F.W. Lewis in 1860s. The Microscopical Society eventually merged with the Biological Section of the ANS to form the Biological and Microscopical Section.

Women could not become ANS members until well into the 20th century. In fact, Ruth Patrick (1907-2013), who had a doctorate based on diatom research at the University of Virginia, wanted to volunteer at the ANS but was kept out for several years. She finally become a volunteer in 1935, serving first as a virtual servant to the Section, setting out specimens for their meetings, among other duties. She eventually became the first woman member of the ANS. In the late 1940s, after she had become a paid employee, Patrick founded the ANS Limnology Department. Through her work, the ANS developed a focus on freshwater diatoms; before that it had collected mostly fossils and saltwater species. She directed studies of rivers and streams, especially in terms of using diatoms to gauge water quality. She collaborated with the noted ecologist Evelyn Hutchinson among others. Her influence lives on in the ANS’s Patrick Center for Environmental Research. Potapova and her associates continue to do both taxonomic and ecological studies on diatoms.  The importance of this work became evident when Potapova mentioned that diatoms are responsible for 20-25% of the earth’s organic carbon fixation.


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