• Category
  • Length Range
    39-66 µm
  • Width Range
    21.6-25.6 µm
  • Striae in 10 µm
  • Synonyms
    Navicula punctata var. asymmetrica Lagerst.
    Navicula gastrum var? styriaca Grunow



Valves are elliptic and curved so that they are slightly asymmetric to the apical axis. In smaller specimens, the valve margins are parallel. Apices are rostrate and rounded. The axial areal is narrow. The central area is bowtie-shaped and bounded by 3-4 short striae of variable length. Raphe branches are both undulate and lateral. The proximal raphe ends are expanded and the terminal raphe ends are deflected toward the primary side of the valve. Striae are radiate and curved toward the valve center throughout. Striae are distinctly punctate, with an areola density of 10-18 in 10 µm.

Cleve (1891) proposed this species based on three syntypes that were previously recognized as varieties: Navicula punctata var. asymmetrica Lagerstedt (1873, p. 29; pl. 2, fig. 7), N. gastrum var? styriaca Grunow (1882, p. 144; pl. 30, fig. 50), and N. gastrum var? styriaca Grunow (Grunow 1884, pl. I, fig. 35). As such, this species awaits lectotypification.


Placoneis amphibola has been reported from a number of locations in North America, although it is typically rare in abundance. It has been reported from Connecticut, Nebraska, Wyoming, Washington, Oregon, and California (Patrick and Reimer 1966). Specimens from West Lake Okoboji, Iowa have been documented (Stoermer 1964), while Foged (1981) reports it from small ponds in Alaska.

A number of forms and varieties have been noted, including Navicula amphibola fo. alaskensis Foged, Navicula amphibola fo. rectangularis Foged (Foged 1981) and Navicula amphibola var. arctica Patrick & Freese (Patrick and Freese 1961). Yet another variety, Navicula amphibola var. perrieri M. Perag. & Héribaud, has been reported from northern Lake Michigan (Stevenson & Stoermer 1978, Stoermer 1980).

The population illustrated on this page was found to be sympatric with a larger, and undetermined, Placoneis with parallel sides, capitate apices and coarse striae and areolae. These larger Placoneis are discontinuous in a size-shape series to the nominate form of P. amphibola.

Placoneis  Morph 1  Landscape  Arb  Ill2017 08
Credit: Mark Edlund, Iowa Lakeside Lab Collection ILL 2017-08, Minnesota Landscape Arboretum
Unidentified Placoneis taxon found to be sympatric with P. amphibola.

Original Description

N. amphibola Cl. — N. punctata var asymmetrica Lagst. II, 7. — N. gastrum var? styriaca Grun. E. Öst. Ung. XXX, 50, 51, F. Jos. Land, I., 35. Foss. Lk. 93. This form seems to be a good species, for which I should have liked to have proposed the name N. styriaca, had not this name been given to another species.

  • Basionym
    Navicula amphibola
  • Author
    Cleve 1891

Original Images

Screen  Shot 2017 06 08 At 8 29 07  Am
Screen  Shot 2017 06 08 At 8 42 01  Am
Screen  Shot 2017 06 08 At 8 43 09  Am

Citations & Links



  • Index Nominum Algarum
  • North American Diatom Ecological Database
    NADED ID: 46474

Cite This Page

Edlund, M., Burge, D. (2017). Placoneis amphibola. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/placoneis_amphibola


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