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Didymosphenia geminata

(Lyngb.) M.Schmidt      Category: Asymmetrical biraphid
BASIONYM: Echinella geminata Lyngb. 1819
SYNONYM(S): Gomphonema geminatum (Lyngb.) C.Agardh 
REPORTED AS: didymo  (common name) | rock snot  (common name) 

Diatomella balfouriana


Diploneis elliptica

LM scalebar = 10 µm = 20 pixels.


Contributor: Sarah Spaulding - November 2010
Length Range: 65-161 µm
Width Range: 36-41 µm
Striae in 10 µm: 7-9 in the center valve


Valves are large, robust and slightly asymmetric to the apical axis. One end of the valve forms a distinct, capitate headpole. The other end of the valve, the footpole, is less capitate to bluntly rounded. The axial area is relatively linear and the central area is an expanded oval. Stigmata number 2-5, with the number of stigmata positively related to valve size. Internally, the stigmata possess convoluted internal occlusions. The raphe is lateral, with expanded proximal raphe ends and deflected distal raphe ends. The distal raphe is deflected near the porefield at the footpole, but does not pass through the porefield. The porefield is large, distinct and composed of fine porelli. The areolae are complex; externally the areolae are within ornamented depressions, internally the areolae open with chambers. The striae are radiate for most of the valve, except near the footpole, where they become nearly parallel. Striae near the valve center are irregular and many do not reach between the central area and valve margin. Under the SEM, a ridge of silica is present between the valve face and margin. This ridge may be expanded into small spines at the headpole.

Didymosphenia geminata is the only species within the genus that has been documented in the lower 48 states, but D. clavaherculis has been documented from Alaska (Metzeltin and Lange-Bertalot, 1995; Pite et al. 2009). Some populations may show greater asymmetry to the apical axis, while others may be nearly linear. The sister taxa to the genus Didymosphenia include Cymbella mexicana and Cymbella janischii (Kociolek and Stoermer 1988).

The range in length posted here is based on measurement of over 90,000 valves over a one year period from South Boulder Creek (Bishop, M.S. Thesis, University of Colorado, 2014).

Original Description

Basionym: Echinella geminata
Author: Lyngb. 1819
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Spaulding, S. (2010). Didymosphenia geminata. In Diatoms of the United States. Retrieved May 23, 2018, from

Species: Didymosphenia geminata

Contributor: Sarah Spaulding

Reviewer: Marina Potapova


Aboal, M., Marco, S., Chaves, E., Mulero, I. and García-Ayala, A. (2012). Ultrastructure and function of stalks of the diatom Didymosphenia geminata. Hydrobiologia. 10.1007/s10750-012-1193-y

Bergey, E.A. and Spaulding, S.A. (2015). Didymosphenia: It’s more complicated. BioScience. 10.1093/biosci/biu226

Blanco, S. and Ector, L. (2009). Distribution, ecology and nuisance effects of the freshwater invasive diatom Didymosphenia geminata (Lyngbye) M. Schmidt: a literature review. Nova Hedwigia 88 (3-4): 347-422. 10.1127/0029-5035/2009/0088-0347

Bothwell, M.L. and Kilroy, C. (2011). Phosphorus limitation of the freshwater benthic diatom Didymosphenia geminata determined by the frequency of dividing cells. Freshwater Biology 56: 565-578. 10.1111/j.1365-2427.2010.02524.x

Kilroy, C. and Bothwell, M. (2011). Environmental control of stalk length in the bloom-forming, freshwater benthic diatom Didymosphenia geminata (Bacillariophyceae). J. Phycol. 47: 981–989. 10.1111/j.1529-8817.2011.01029.x

Kilroy, C. and Bothwell, M.L. (2012). Didymosphenia geminata growth rates and bloom formation in relation to ambient dissolved phosphorus concentration. Freshwater Biology 57: 641-653. 10.1111/j.1365-2427.2011.02727.x

Kirkwood, A.E., Shea, T., Jackson, L.J. and McCauley, E. (2007). Didymosphenia geminata in two Alberta headwater rivers: an emerging invasive species that challenges conventional views on algal bloom development. Can. J. Fish. Aquat. Sci. 64:1703–9.

Kociolek, J.P. and Stoermer, E.F. (1988). A preliminary investigation of the phylogenetic relationships among the freshwater, apical porefield-bearing cymbelloid and gomphonemoid diatoms (Bacillariophyceae). Journal of Phycology 24: 377-385. 10.1111/j.1529-8817.1988.tb04480.x

Kumar, S., Spaulding, S.A., Stohlgren, T., Hermann, K., Schmidt, T. and Bahls, L. (2009). Modelling the bioclimatic profile of the diatom Didymosphenia geminata. Frontiers in Ecology and the Environment 8: 415-420. 10.1890/080054

Lyngbye, H.C. (1819). Tentamen Hydrophytologiae Danicae Continens omnia Hydrophyta Cryptogama Daniae, Holsatiae, Faeroae, Islandiae, Groenlandiae hucusque cognita, Systematice Disposita, Descripta et iconibus illustrata, Adjectis Simul Speciebus Norvegicis. Hafniae. 248 pp.

Metzeltin, D. and Lange-Bertalot, H. (1995). Kritishe Wertung der Taxa in Didymosphenia (Bacillariophceae). Nova Hedwigia 60: 381-405.

Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

Pite, D., Lane, K., Hermann, A, Spaulding, S.A. and Finney, B. (2009). Historical abundance and morphology of Didymosphenia geminata in Naknek Lake, Alaska. Proceedings of the 20th International Diatom Symposium, Acta Bot. Croat. 68: 183-197.

Reid, B.L., Hernández, K.L., Frangópulos, M., Bauer, G., Lorca, M., Kilroy, C. and Spaulding, S.A. (2012). The invasion of the freshwater diatom Didymosphenia geminata in Patagonia: prospects, strategies, and implications for biosecurity of invasive microorganisms in continental waters. Conservation Letters.

Schmidt, A. (-). (1874-1959). Atlas der Diatomaceen-Kunde, von Adolf Schmidt, continued by Martin Schmidt, Friedrich Fricke, Heinrich Heiden, Otto Muller, Friedrich Hustedt. Reprint 1984, Koeltz Scientific Books, Konigstein, 480 plates.

Spaulding, S.A., Kilroy, C. and Edlund, M. (2010). Diatoms as invasive species. In: Smol, J. & E.F. Stoermer (eds). The Diatoms: Applications for the Environmental and Earth Sciences. Cambridge University Press, Cambridge. pgs. 560-569.

Taylor, B.W. and Bothwell, M.I. (2014). The origin of invasive microorganisms matters for science, policy, and management: The case of Didymosphenia geminata . BioScience 64: 531–538.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA

California Academy of Sciences (CAS)

Didymosphenia geminata CAS

NCBI Genbank Taxonomy

Didymosphenia geminata NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 81001

Autecology Discussion

Didymosphenia geminata is known by the common name, ‘didymo’. It attaches by a mucopolysaccaride stalk to benthic substrates in flowing waters and splash zones of lakes. In some rivers, cells of D. geminata produce large amounts of stalk, so large that river bottoms may become covered by a thick felt. The stalks may become long and stringy, forming white strands up to 1 meter long. Such nuisance “blooms” have been increasing in extent in North America and Europe (Blanco and Ector 2009). In New Zealand, Chile and Argentina D. geminata is an invasive organism (Kilroy and Bothwell 2011, Reid et al. 2012).

Bothwell first presented the compelling paradox that nuisance blooms of D. geminata occur only in oligotrophic rivers, and the observation has since been elaborated on by others (Kirkwood et al. 2007, Kilroy and Bothwell 2011). The observation of high biomass in low nutrient waters goes against the traditional positive relationship of algal biomass and nutrient concentration. The causes of large amounts of stalk production by this diatom have been understood as either “photosynthetic overflow” (Kilroy and Bothwell 2011) or as a means for uptake of phosphorus (Sundareshwar et al. 2011). Further work is needed to resolve the role of stalk production in D. geminata and the understanding the global expansion of this diatom and the ecologically important role of stalk production in the diatoms as a whole.


Live cell of Didymosphenia geminata, showing the golden brown chloroplast. A number of cells of Achnanthidium are attached to the mucilage stalk.

Credit/Source: Sarah Spaulding

Live cell of Didymosphenia geminata showing the mucilage stalk.

Credit/Source: Sarah Spaulding

Numerous cells and mucilage stalks from South Boulder Creek, November 2011.

Credit/Source: Sarah Spaulding

Small tufts of Didymosphenia geminata cells (approximately 2 cm across) in South Boulder Creek, October 2010. Cells often grow in the splash zone of streams and rivers.

Credit/Source: Sarah Spaulding

Bloom of Didymosphenia geminata in the Rio Espolón, Chile in 2010. Largest cobbles are approximately 20 cm in diameter. The bloom shows the characteristic golden brown color of the cells, which are attached to the cobbles by the mucilagious stalk.

Credit/Source: Sarah Spaulding

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Didymosphenia geminata

EMAP Response Plots

Didymosphenia geminata

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.