• Category
  • Length Range
    45-68 µm
  • Width Range
    1.1-4.5 µm
  • Striae in 10 µm



Valves are long and narrow, with capitate apices. Valves are distinctly heteropolar, or may have asymmetric margins, variable within a population. The central sternum is very narrow and may not be distinguishable. The striae are uniseriate and somewhat irregularly spaced. The striae are slightly off-set from one another at the central sternum. Marginal spines may, or may not be present. A single rimoportula is present at the footpole (larger apex). The spines may also be irregularly spaced. In SEM, the spines can be seen to be positioned between the striae. A small apical porefield is present on the margin of the footpole.

Living cells are joined in colonies, linked valve face to valve face, at the footpole by mucilage pads. Asterionella formosa is a common diatom in the plankton of lakes and slow moving rivers.

A rimoportula may be present at either pole, at both poles, or even more than one rimoportula at a pole (Körner 1969, Round et al. 1990). Transmission electron micrographs further show porefields at both apices (Körner 1969). Patrick and Reimer (1966) report maximum valve length of 130 µm in US specimens. Körner (1970) considers A. gracillima to be synonymous with A. formosa. A number of varieties are treated in the same reference by Körner.


Asterionella formosa is common in mesotrophic and eutrophic lakes globally and is one of the most common planktonic diatoms in these lakes in the northern hemisphere. Studies of the seasonality of A. formosa date to the classic works of Lund (1950) in Windemere.

In North America, populations of A. formosa, along with Fragilaria crotonensis Kitton, have been shown to increase greatly with increases of reactive nitrogen (Nr) in oligotrophic alpine lakes of the Rocky Mountains. This increase has been interpreted as a response to atmospheric nutrient enrichment (Saros et al. 2005, Saros et al. 2010). Many diatoms in low nutrient lakes respond with population increases even with relatively low loads of reactive nitrogen. In particular, A. formosa has been used as a marker of “critical loads”, defined as the threshold of the nitrogen deposition rate above which there is a discernible ecological effect (Porter and Johnson 2007).

Although A. formosa is common in mesotrophic and eutrophic lakes globally, it has been increasing in presence and abundance in oligotrophic alpine lakes. This increase is interpreted as a response to atmospheric nutrient enrichment. Diatoms respond, even to relatively low loads of anthropogenic reactive nitrogen, in low nutrient lakes. In particular, A. formosa has been a marker of "critical loads", defined as the threshold of nitrogen deposition rate below which there is no discernible ecological effect (Porter and Johnson 2007). For example, relative abundance of A. formosa in Rocky Mountain National Park lake sediments approaches 60% in some lakes (Wolfe et al. 2003), 20-25% in lakes of the Beartooth Mountains (Saros et al. 2010) and to a lesser extent in shallow lakes of the Tetons (Spaulding et al. 2015). Hoh Lake, in western Washington, increased to more than 20% A. formosa in response to an estimated summer bulk deposition load of 1.0± 0.3 kg N ha-1 yr-1 (Sheibley et al. 2014).

Asterionella formosa
Credit: Jan Parmentier
Asterionella formosa lives in colonies, joined by mucilage pads. The elongate shape of the frustules and the spiral colonies are resistant to sinking in their planktonic habitat.

Original Description

  • Author
    Hassall 1850

Citations & Links



Cite This Page

Spaulding, S. (2012). Asterionella formosa. In Diatoms of North America. Retrieved April 16, 2024, from https://diatoms.org/species/asterionella_formosa


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Asterionella formosa from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.