Just over a year ago I had a stroke. It affected my speech and several times a day the nurse or therapist would check on my progress and have me repeat very specific phrases: “baseball”, “huckleberry”, “no ifs, ands, or buts about it”, “fifty-fifty”. Every time I said that last one, it made me think of a couple projects I was working on. Fifty-fifty. Fifty years or fifty million years? Sometimes that’s how long it takes to solve scientific questions.

Figure 1. Dr. Gene Stoermer worked and taught at Iowa Lakeside Lab, where he discovered polymorphic Mastogloia.

Fifty years ago, my PhD advisor, Dr. Gene Stoermer (Figure 1), published a short paper showing how, in a small wetland in Iowa (USA), a single Mastogloia cell could be identified as two completely different diatom species, depending on how you looked at it under your microscope (Stoermer 1967). Diatoms are single-celled algae that have a two-part glass cell wall surrounding them—like a Petri dish, only microscopic. For that diatom in the Iowa wetland, it is easy to recognize the separated halves of the Petri dish as either Mastogloia grevilleior as Mastogloia danseyi (Figure 2). But sometimes, when seen in girdle view, one half of the cell wall looked like one species, while the other half looked like a completely different species—a Janus cell (Andrejić et al. 2018), named for the Roman god often portrayed with two faces. That’s not normal for diatoms.

Figure 2. The 50-year mystery—under certain conditions Mastogloia danseyi (left) shifts its morphology to Mastogloia grevillei (right). The two different forms expressed on each valve of the same cell is clearly evident in girdle view (middle).

Fifty million years ago, the world was living under our doomsday climate scenario, the Eocene hot house. It was about this time that diatoms invaded fresh waters from the marine to eventually colonize every pond, lake, and stream in the world. But finding freshwater Eocene deposits with diatoms is rare. In Canada’s Northwest Territories, funky geologic deposits called diatremes that formed in the Eocene can be found—think a deep, narrow volcanic crater that became a lake after the volcano erupted. We were interested in what this hot house climate was like, what was in these early lakes, and how the early diatoms fit in.

Figure 3. The Czar, Dr. Dave Czarnecki, was the first to show Mastogloia danseyi could switch to M. danseyi fo. grevillei in culture.

Recently, working with great colleagues, we solved the 50/50 mysteries in Plant Ecology & Evolution, in a special issue honoring the service, training, and research contributions of Dr. Eileen Cox. With David Burge from our St. Croix Watershed Research Station, we solved the 50-year problem by showing that clones of Mastogloia from both Iowa and Minnesota could be forced to switch between the two “species” by adding or removing salts from the cultures (Edlund and Burge 2019), a phenomenon first studied by the “Czar”, Dr. Dave Czarnecki (Figure 3), and his students. This was in fact a rare example of a diatom “polyphenism”, a diatom that could completely switch its identity following an environmental trigger (Andrejić et al. 2018). Since these two “species” are obviously just one, the oldest name for this taxon, Mastogloia danseyi, takes priority, and the the “grevillei” morphology became recognized as an ecophenotype or forma, Mastogloia danseyi fo. grevillei. This species may prove to be the perfect nanotechnology candidate to study how diatoms control their incredibly intricate patterns.

Figure 4. The 50-million year mystery—Aulacoseira giraffensis was an early colonizer of lakes during the Eocene hothouse.

In the same issue, partnering with Connecticut College and University of Alberta researchers Drs Peter Siver and Alex Wolfe and others, we described an unknown 50-million-year-old species of diatom that dominated the “Giraffe Pipe” Eocene paleolake (Siver et al. 2019). Aulacoseira giraffensis (Figure 4) didn’t look that much different than modern Aulacoseiraspecies we see in our Minnesota lakes, suggesting that this early colonizer of fresh waters already had a similar structure, cell plan, and life history strategy that we see so successful in modern Aulacoseiraspecies. The well-preserved diatoms, chrysophytes, sponges, amoebae, and plant fossils found in these Eocene diatremes have provided unparalleled material for understanding early colonization of fresh waters and conditions during the Eocene hothouse (P. A. Siver and Wolfe 2009; Barber, Siver, and Karis 2013; Wolfe et al. 2012; 2006). If only the diatoms in those Eocene deposits were worth as much as what everyone was really looking for in those Eocene samples—diamonds!

Fifty-fifty. My speech was worth much more to me than any Eocene diamonds, and after a few days in the hospital, thankfully I could talk normally again. But I couldn’t sing. I couldn’t sing before the stroke either, and I don’t think another 50 years or 50 million years will solve that problem.


Mark was able to prepare this post because of some extra stay-at-home time during the coronavirus pandemic. If you have some time to fill and would like to use it to tell the world about your diatom work, consider writing us a blog post! We hope you are all staying safe and healthy during these stressful times.


Mark Edlund is a senior researcher associated with the University of Minnesota. Email Mark or drop message below if you have any questions about the post.



  • Andrejić, Jelena Z., Sarah A. Spaulding, Kalina M. Manoylov, and Mark B. Edlund. 2018. “Phenotypic Plasticity in Diatoms: Janus Cells in Four Gomphonema Taxa.” Diatom Research 33 (4): 453–70.
  • Barber, Andrew, Peter A. Siver, and William Karis. 2013. “Euglyphid Testate Amoebae (Rhizaria: Euglyphida) from an Arctic Eocene Waterbody: Evidence of Evolutionary Stasis in Plate Morphology For Over 40 Million Years.” Protist 164 (4): 541–55.
  • Edlund, Mark B., and David R. L. Burge. 2019. “Polymorphism in Mastogloia (Bacillariophyceae) Revisited.” Plant Ecology and Evolution 152 (2): 351–57.
  • Siver, P. A., and A. P. Wolfe. 2009. “Tropical Ochrophyte Algae From the Eocene of Northern Canada: A Biogeographic Response To Past Global Warming.” Palaios 24 (3): 192–198.
  • Siver, Peter A., Alexander P. Wolfe, Mark B. Edlund, Joel Sibley, Josh Hausman, Paula Torres, and Anne Marie Lott. 2019. “Aulacoseira Giraffensis (Bacillariophyceae), a New Diatom Species Forming Massive Populations in an Eocene Lake.” Plant Ecology and Evolution 152 (2): 358–67.
  • Wolfe, Alexander P., Adam Z. Csank, Alberto V. Reyes, Ryan C. McKellar, Ralf Tappert, and Karlis Muehlenbachs. 2012. “Pristine Early Eocene Wood Buried Deeply in Kimberlite from Northern Canada.” PLoS One 7 (9).
  • Wolfe, Alexander P., Mark B. Edlund, Arthur R. Sweet, and Steven D. Creighton. 2006. “A First Account of Organelle Preservation in Eocene Nonmarine Diatoms: Observations and Paleobiological Implications.” PALAIOS 21 (3): 298–304.