• Category
  • Length Range
    104.6-192.2 µm
  • Width Range
    1.5 to 2.8 at the valve center µm
  • Striae in 10 µm



Valves heteropolar and linear. Headpole is capitate and ends bluntly truncated, 3.1 to 3.7 µm wide. Foot pole is rostrate, ending rounded, 1.3 to 1.6 µm wide, not as wide as the valve center. Rimoportulae present in the headpole. Striae very fine, not easily resolved in LM. Spines can be faint in LM, occurring at the valve margin 6 to 7 in 10 µm. In girdle view, the head pole is expanded in the pervalvar axis.


This taxon is commonly found in the plankton forming stellate colonies in northern, low pH lakes and ponds of the northeastern United States (Körner 1970, Camburn and Charles 2000, Siver et al. 2005) and Canada (Fallu et al. 2000). Here we observed A. ralfsii var. americana from Partridge Lake in the Boundary Waters Canoe Area Wilderness of northern Minnesota.

Original Description

It differs from the nominate variety and the other variety by the triangular shaped foot pole, the smaller transapical width in the middle of the valve and by the distinct geographical distribution; besides to be distinguished by means of the electronic microscope by the broad pseudoraphe.

  • Author
    Körner 1970
  • Length Range
    20-90 µm
  • Width
    1-5 µm
  • Striae in 10µm

Original Images

Asterionella ralfsii var. americana orig illus
Asterionella ralfsii var. americana orig descr

Cite This Page

Burge, D., Edlund, M. (2017). Asterionella ralfsii var. americana. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/asterionella_ralfsii_var._americana


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Asterionella ralfsii var. americana 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.