• Category
  • Diameter
    6-30 µm
  • Width Range
    5-15 µm



Cells are cylindrical, forming chains. Frustules are 6-30 µm in diameter with a mantle height of 5-15 µm. The valve face is slightly convex, covered with small spines. The mantle is covered by small granules. The frustule has a loculate structure. Numerous rimoportulae are scattered over valve face and mantle and one row of rimoportulae occurs on the mantle edge.


Melosira varians is very common in rivers and lakes across North America. This species is considered to be tolerant of poor water quality, although it may occur in more pristine sites as well. This diatom is primarily found in benthic habitats, with cells joined in long filamentous chains. Both individual cells and filaments may become entrained in the plankton.

Melosira Varians
Credit: Mark Edlund
Living cells of M. varians grow in long filaments

Original Description

Meloseira varians, caespite fusco fluctuante, filis crassitie variis fragilissimis aureis, articulis diametro aequalibus, geniculis contractis interdum aequalibus et tunc genicula simulantibus.

  • Author
    C.Agardh 1827

Original Images

Melos Varians  Orig Descr

Cite This Page

Potapova, M. (2009). Melosira varians. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/melosira_varians


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