• Category
  • Length Range
    42.3-71.4 µm
  • Width Range
    2.6-3.9 µm
  • Striae in 10 µm
  • Synonyms
    Synedra amphicephala Kütz.
    Fragilaria capucina ssp. amphicephala (Kütz.) Lange-Bert.
    Fragilaria amphicephala Ehrenb.
  • Reported As
    Fragilaria capucina var. amphicephala (Krammer & Lange-Bertalot 1991, p. 125, Pl. 109, Figs. 19, 20)



Valves are linear-lanceolate. The apices are narrowly attenuate, with capitate ends. The central area is variable, from bilaterally expanded to weakly unilaterally expanded. In some specimens, the central area is slightly tumid. Striae may absent from the central area, or ghost striae may be present. Striae are parallel, mostly alternate, occurring 11-12 in 10 µm. Striae are interrupted by a narrow axial area, which widens near the central area. Areolae are fine, and not visible in LM. Spines are absent.

This taxon was originally described by Kützing (1844, pg. 64, Pl. 3, fig. 12) as Synedra amphicephala. Later, it was later transferred to the subspecies Fragilaria capucina ssp. amphicephala (Lange-Bertalot 1993, p. 44). Note that Fragilaria capucina var. amphicephala (Krammer & Lange-Bertalot 1991, p. 125, Pl. 109, Figs. 19, 20) is invalid because the baysionym was properly referenced. Finally, it was elevated to the species rank (Hofmann et al. 2011: p. 256, Pl. 7, figs. 7-10).


The specimens shown here were collected in Idaho. It has been reported as being widely distributed across the US (Patrick and Reimer 1966), as Synedra amphicephala var. amphicephala. In Europe, it has been reported in oligotrophic to mesotrophic lakes of the Alps and foothills of southern Germany, with few occurrences in rivers and the lowlands of northern Germany (Hofmann et al. 2013) .

Original Description

  • Author
    Lange-Bert. 2011
  • Length Range
    40-75 µm
  • Width
    2-3 µm
  • Striae in 10µm

Original Images

Fragilaria amphicephaloides orig illus

Cite This Page

Burge, D. (2015). Fragilaria amphicephaloides. In Diatoms of North America. Retrieved August 19, 2018, from https://diatoms.org/species/fragilaria_amphicephaloides


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Fragilaria amphicephaloides 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.