Diatoms are single‐celled autotrophic organisms with highly ornate siliceous walls. They account for more than 20% of the world's primary production, are responsible for much of the petroleum humans use, and deposits of their shells are mined for numerous uses. The most taxonomically diverse groups of photosynthetic protists, diatoms are of ecological importance in nearly every freshwater and marine habitat. Their closest relatives are a poorly known group of microflagellates, some silicified and some not. Efforts to reconstruct diatom phylogeny are hampered by the fact that their true diversity and that of their closest relatives remains unknown. Genomic studies are creating tremendous new opportunities for study of this important group. Perhaps as much as a third of the diatom nuclear genome is now thought to be recently laterally transferred from bacteria. Diatom adaptation to such a wide range of environments may be a result of the resulting novel gene combinations.

Key Concepts:

  • Diatoms are a highly diverse group of protists, with perhaps more than 200 000 species, most of which remain undescribed.

  • There are four major structural groups, radial centrics, polar centrics, araphid pennates and raphid pennates.

  • Among the four major structural groups of diatoms, only the raphid pennates are robustly supported as monophyletic.

  • Diatoms dominate the world's oceans, lakes and streams, conducting more than 20% of the world's photosynthesis.

  • Diatoms are critical indicators of aquatic ecosystem conditions, past and present.

  • Fossil diatoms have significant economic importance as stratigraphic indicators for mineral exploration, particularly petroleum and as a source of diatomite, which is used in numerous industrial applications.

  • Diatoms make a diverse number of nanoscale siliceous structures, an order of magnitude smaller than that presently attainable by human technology.

  • Understanding how diatoms make their shells may lead to breakthroughs in nanotechnology.

  • Nearly a third of the diatom nuclear genome appears to be the result of relatively recent horizontal gene transfer from bacteria.

  • Horizontal gene transfer may play a role in the apparent rapid adaptation and diversification of diatoms.

Keywords: diatoms; protists; heterokont algae; stramenopiles; freshwater ecology; marine biology; genomics; horizontal gene transfer; indicator organisms; nanotechnology

Figure 1.

Generalised diatom life history. OE, original epivalve; OH, original hypovalve.

Figure 2.

Scanning electron micrograph of a plankton diatom assemblage from Lake Michigan, USA. The diatom dominating the centre is a centric diatom (genus Stephanodiscus). Numerous araphid pennate diatoms (genus Asterionella) are also visible, as is another centric diatom (genus Aulacoseira) at the bottom. For the most part, only valves are visible here, as the cell walls were disrupted by acid cleaning, a common preparation technique for better viewing in the scanning electron micrograph. For scale, the Stephanodiscus cell is approximately 50 μm in diameter. Species of this genus almost always have radiating ribs ending in a spine, as visible here. In contrast to Stephanodiscus, the cells of Aulacoseira are typically much taller than they are wide, and so appear as tubes rather than discs. The valves of Asterionella are long and thin, but end in a slightly pinched and then expanded tip. All these variations and much more occur in the minute valves of diatoms (see Round et al., ).

Figure 3.

Phylogenetic relationships of large structurally defined groups of diatoms based on maximum likelihood analysis of SSU, rbcL and psbC genes (see Theriot et al., for details). Representative taxa of larger clades are indicated by triangles. Long tubular diatoms such as Aulacoseira (Figure ) form a grade at the base of the diatom tree. Most discoid radial centrics are found in a single clade. But these are not the only places on the tree where such shapes occur. Polar centrics include diatoms of a wide variety of shapes and forms, from star‐shaped cells, to cells with long tubular shape (such as Stictocyclus), and cells with a flat discoid shape such as Stephanodiscus (Figure ).

Figure 4.

Stages of periphyton development on glass‐slide substrates from Pawnee Reservoir, Nebraska. (a) Typical development after 2 weeks of submersion; diatoms and other microalgae are attached directly to the glass. (b) After 5 weeks, an upper story of diatoms on long stalks has developed, completely overgrowing all lower canopies. Bar, 100 μm. Photographs courtesy of Kyle Hoagland.

Figure 5.

Diagram of succession in a periphyton ‘forest’. (a) Attached bacteria; (b) Navicula menisculus var. upsaliensis – prostrate attachment, mucilage coat; (c) Gomphonema parvulum – short stalks; (d) Gomphonema parvulum – long stalks; (e) Fragilaria vaucheriae – rosette, mucilage pads; (f) Synedra acus – large rosette, mucilage pads; (g) Nitzschia sp. – rosette, mucilage pads; and (h) Stigeoclonium sp. – upright filaments. Reprinted with permission from Hoagland et al. . Copyright © 1982 Botanical Society of America.



Alverson AJ (2008) Molecular systematics and the diatom species. Protist 159: 339–353.

Alverson AJ, Beszteri B, Julius ML and Theriot EC (2011) The model marine diatom Thalassiosira pseudonana likely descended from a freshwater ancestor in the genus Cyclotella. BMC Evolutionary Biology 11.

Anderson RA, Medlin L and Crawford RM (1986) An investigation of cell wall components of Actinocyclus subtilis (Bacillariophyceae). Journal of Phycology 22: 466–484.

Armbrust EV (2009) The life of diatoms in the world's oceans. Nature 459: 185–192.

Armbrust EV, Berges JA, Bowler C et al. (2004) The genome of the diatom Thalassiosira pseudonana: ecology evolution and metabolism. Science 306: 79–86.

Bowler C, Allen AE, Badger JH et al. (2008) The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456: 239–244.

Bradbury J (2004) Nature's nanotechnologists: unveiling the secrets of diatoms. PLoS Biology 2: e306.

Cavalier‐Smith T (1986) The Kingdom Chromista: origin and systematics. Progress in Phycological Research 4: 309–347.

Charles DF, Battarbee RW, Renberg I, van Dam H and Smol JP (1989) Paleoecological analysis of lake acidification trends in North America and Europe using diatoms and chrysophytes. In: Norton SA, Lindberg SE and Page A (eds) Biological Monitoring of Freshwater Ecosystems, pp. 233–293. Boca Raton, FL: CRC Press.

Conley DJ, Kilham SS and Theriot E (1989) Variation in the silica content of diatoms: differences between marine and freshwater diatoms. Limnology and Oceanography 34: 205–213.

Daugbjerg N and Guillou L (2001) Phylogenetic analyses of Bolidophyceae (Heterokontophyta) using rbcL gene sequences support their sister group relationship to diatoms. Phycologia 40: 153–161.

Fritz SC, Juggins S, Battarbee RW and Engstrom DR (1991) Reconstruction of past changes in salinity and climate using a diatom‐based transfer function. Nature 352: 52–54.

Goertzen LR and Theriot EC (2003) Effect of taxon sampling, character weighting, and combined data on the interpretation of relationships among the heterokont algae. Journal of Phycology 39: 423–439.

Gordon R, Losic D, Tiffany MA, Nagy SS and Sterrenburg FA (2009) The glass menagerie: diatoms for novel applications in nanotechnology. Trends in Biotechnology 27: 116–127.

Guillou L, Chrétiennot‐Dinet M‐J, Medlin LK et al. (1999) Bolidomonas: a new genus with two species belonging to a new algal class, the Bolidophyceae (Heterokonta). Journal of Phycology 35: 368–381.

Hoagland KE, Roemer SC and Rosowski JR (1982) Colonization and community structure of two periphyton assemblages, with emphasis on the diatoms (Bacillariophyceae). American Journal of Botany 69: 188–213.

Holba AG, Dzou LIP, Masterson WD et al. (1998) Application of 24‐norcholestanes for constraining source age of petroleum. Organic Geochemistry 29: 1269–1283.

Ichinomiya M, Yoshikawa S, Kamiya M et al. (2011) Isolation and characterization of Parmales (Heterokonta/Heterokontophyta/Stramenopiles) from the Oyashio Region, Western North Pacific. Journal of Phycology 47: 144–151.

Interlandi SJ and Kilham SS (2001) Limiting resources and the regulation of diversity in phytoplankton communities. Ecology 82: 1270–1282.

Julius ML and Theriot EC (2010) The diatoms: a primer. In: Smol J and Stoermer EF (eds) The Diatoms: Applications for the Environmental and Earth Sciences, pp. 8–22. Cambridge: Cambridge University Press.

Kilham SS, Theriot EC and Fritz SC (1996) Linking planktonic diatoms and climate change using resource theory in the large lakes of the Yellowstone ecosystem. Limnology and Oceanography 41: 1052–1062.

Leipe DD, Wainright PO, Gunderson HJ et al. (1994) The stramenopiles from a molecular perspective: 16S‐like rRNA sequences from Labyrinthuloides minuta and Cafeteria roenbegensis. Phycologia 33: 369–377.

Luther A (1899) Über Chlorosaccus eine neue Gattung der Süsswasseralgen. Bih. Svenska Vet‐Akademische Handlungen 24, Afd. III 13: 1–22.

Mann DG and Droop SJM (1996) Biodiversity, biogeography and conservation of diatoms. In: Kristiansen J (ed.) Biogeography of Freshwater Algae: Proceedings of the Workshop on Biogeography of Freshwater Algae, Developments in Hydrobiology, pp. 19–32. Dordecht: Kluwer Academic Publishers.

Mann DG and Evans KM (2007) Molecular genetics and the neglected art of diatomics. In: Brodie J and Lewis J (eds) Unravelling the Algae – the Past, Present and Future of Algal Systematics, pp. 231–265. Boca Raton, FL: CRC Press.

Mann DG and Marchant HJ (1989) The origins of the diatom and its life cycle. In: Green JC, Leadbeater BSC and Diver WI (eds) The Chromophyte Algae: Problems and Perspectives, pp. 307–323. Oxford: Clarendon Press.

Medlin LK (2010) Pursuit of a natural classification of diatoms: an incorrect comparison of published data. European Journal of Phycology 45: 155–166.

Nelson DM, Treguer P, Brzezinski MA, Leynaert A and Queguiner B (1995) Production and dissolution of biogenic silica in the ocean – revised global estimates, comparison with regional data and relationship to biogenic sedimentation. Global Biogeochemical Cycles 9: 359–372.

Parfrey LW, Lahr DJG, Knoll AH and Katz LA (2011) Estimating the timing of early eukaryotic diversification with multigene molecular clocks. Proceedings of the National Academy of Sciences 108: 13624–13629.

Patterson DJ (1989) Stramenopiles: chromophytes from a protistan perspective. In: Green JC, Leadbeater BSC and Diver WI (eds) The Chromophyte Algae: Problems and Perspectives. The Systematics Association Special Volume, 38, pp. 357–379. Oxford: Clarendon Press.

Rothpletz A (1896) Über die Flysch‐Fucoiden und einige andere fossile Algae, sowie über laisische, Diatomeen führende Hornschwämme. Zeitschrift der Deutschen Geologischen Gesellschaft 4: 854–914.

Rothpletz A (1900) Über einen neuen jurassichen Hornschwämme unddie darin eingeschlossenen Diatomeen. Zeitschrift der Deutschen Geologischen Gesellschaft 52: 154–160.

Round FE (1981) Some aspects of the origin of diatoms and their subsequent evolution. Biosystems 14(3–4): 483–486.

Round FE and Crawford RM (1981) The lines of evolution of the Bacillariophyta. 1. Origin. Proceedings of the Royal Society of London Series B‐Biological Sciences 211(1183): 237–260.

Round FE and Crawford RM (1984) The lines of evolution of the Bacillariophyta. 2. The Centric Series. Proceedings of the Royal Society of London Series B‐Biological Sciences 221(1223): 169–188.

Round FE, Crawford RM and Mann DG (1990) The Diatoms, Biology and Morphology of the Genera. Cambridge: Cambridge University Press.

Saros JE and Fritz SC (2000) Nutrients as a link between ionic concentration/composition and diatom distributions in saline lakes. Journal of Paleolimnology 23: 449–453.

Sinninghe‐Damste JS, Muyzer G, Abbas B et al. (2004) The rise of the rhizosolenid diatoms. Science 304: 584–587.

Smol JP and Stoermer EF (eds) (2010) The Diatoms: Applications for the Environmental and Earth Sciences, 2nd edn. New York: Cambridge University Press.

Sorhannus U (2007) A nuclear‐encoded small‐subunit ribosomal RNA timescale for diatom evolution. Marine Micropaleontology 65: 1–12.

Stoermer EF, Wolin JA, Schelske CL and Conley DJ (1990) Siliceous microfossil succession in Lake Michigan. Limnology and Oceanography 35: 959–967.

Sullivan MJ and Moncreiff CA (1988) Primary production of edaphic algal communities in a Mississippi salt marsh. Journal of Phycology 24: 49–58.

Theriot EC, Ashworth M, Nakov T, Ruck EC and Jansen RK (2010) A preliminary multigene phylogeny of the diatoms (Bacillariophyta): challenges for future research. Plant Ecology and Evolution 143: 278–296.

Theriot EC, Ruck EC, Ashworth M, Nakov T and Jansen RK (2011) Status of the pursuit of the diatom phylogeny: are traditional views and new molecular paradigms really that different? In: Seckbach J and Kociolek JP (eds) The Diatom World: 600. Springer.

Weerman EJ, Herman PMJ and Van De Koppel J (2010) Top‐down control inhibits spatial self‐organization of a patterned landscape. Ecology 92: 487–495.

Werner D (ed.) (1977) The Biology of Diatoms. Botanical Monographs vol. 13. Berkeley: University of California Press.

Williams DM and Kociolek JP (2007) Pursuit of a natural classification of diatoms: history, monophyly and the rejection of paraphyletic taxa. European Journal of Phycology 42: 313–319.

Further Reading

Bowler C, Vardi A and Allen AE (2010) Oceanographic and biogeochemical insights from diatom genomes. Annual Review of Marine Science 2: 333–365.

Seckbach J and Kociolek JP (eds) (2011) The Diatom World. Cellular Origin, Life in Extreme Habitats and Astrobiology, vol. 19. Dordrecht: Springer.

Theriot E (1992) Clusters, species concepts and morphological evolution of diatoms. Systematic Biology 41: 141–157.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Theriot, Edward C(Mar 2012) Diatoms. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000330.pub2]