• Category
  • Length Range
    23.6-31.1 µm
  • Width Range
    8.1-8.7 µm
  • Striae in 10 µm
  • Synonyms
    Oestrupia zachariasii var. undulata (Schulz) Stoermer and Yang



Valves are linear-lanceolate, with a tri-undulate margin. The central undulation is the broadest point of the undulations. Apices are cuneate. The axial area is linear and narrow. The central area is slightly expanded, to round in larger specimens. Each stria is composed of three transapically elongate openings (with the most distal often placed on the valve mantle). The distal two openings are connected by an alveolate chamber that forms a marginal longitudinal line. Striae are parallel in the central valve and radiate toward the valve ends. The raphe is straight and filiform, with straight proximal ends. Distal raphe ends are both hooked to the same side.


Biremis undulata is a truly rare diatom and has been reported only a handful of times in North America. It appears limited in its distribution to benthic habitats in oligotrophic to mesotrophic lake systems. In North America it has been reported from northern Lake Michigan and large inland lakes of Michigan’s northern lower peninsula (Stoermer & Yang 1969, Anderesen & Stoermer 1978, Stoermer 1978, 1980, Edlund et al. 2001).

Original Description

Var. undulata n.v. (Fig. 77). - Schalen linear-elliptisch mit undulierten Seiten und deutlich keilförmigen Enden. Streifen aus transapikal verlängerten Punkten bestehend, die 3 wellige Längslinien bilden. Punkte der inneren Reihen besonders stark verlängert. Randlinien nicht besonders deutlich, dicht am Schalenrande. Grösse 36 : 11 µ, Str. 10 - 11. Heiternest (49 - 52 m).

  • Basionym
    Caloneis baltica var. undulata
  • Author
    P.Schulz 1926
  • Length Range
    36 µm
  • Width
    11 µm
  • Striae in 10µm

Original Images

Type  Caloneis Baltica V  Undulata  Schulz 1926
Caloneis baltica var. undulata orig illus

Cite This Page

Edlund, M., Burge, D. (2017). Biremis undulata. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/biremis_undulata


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