• Category
  • Diameter
    33.9-62.9 µm
  • Width Range
    13.5-21.7 µm
  • Synonyms
    Melosira undulata var. normanii (Arnott ex Van Heurck) De Toni 1894
  • Reported As
    Cyclotella fottii (Reavie and Smol 1998)



Cells are large, heavily-silicified and arranged in short filaments of 2-15 cells. The mantle height is variable, with larger cells having comparably shorter mantles. The valve face is flat to slightly convex and meets the mantle at a right angle. The valve face has a small central area, with scattered areolae. The central area is surrounded by spirally arranged and anastamosing rows of coarse areolae (areolae number 14-21 in 10 µm). Striae continue onto the valve mantle, where they are arranged in straight pervalvar rows (14.5-16.7 striae in 10 µm) with a areolae density similar to that on the valve face. The mantle has multiple, large rimoportulae which are located closer to the valve face than to the mantle margin. The rimportulae are regularly spaced. In valve view, deep focus on the inner outline of the mantle shows a characteristic polygonal outline. In girdle view, deep focus shows a thick, bullulate cell wall structure.


Melosira normannii is not regularly encountered in collections. It prefers oligo- to mesotrophic waters and seems to be more common in more northerly regions. It is a benthic diatom and seems to prefer deep, sandy or fine-grained sediments. Material illustrated here comes from northern Minnesota boreal lakes, a lake in Isle Royale National Park, and from epipsammon on the St. Croix River, Minnesota-Wisconsin. Below are living cells of Melosira undulata var. normannii showing how their short filaments produces large mucilage strands that hold cells among sand grains (St. Croix River, MN). Stoermer (1980) illustrates specimens from Lake Michigan and Lake Superior and notes that it is found in regions that are isolated from direct pollution sources and that its primary habitat is epipelon. Stoermer and Yang (1969) report in Lake Michigan that it is rare in the plankton, can be found as deepwater periphyton, and that the "var. normannii" is more northern than the nominate varety. Reavie and Smol (1998) found it rare in sediment cores from the St. Lawrence River and that it was not observed in modern material.

9  Live  Melo Undu Norm Stalks  St  Croix Riv
Credit: Mark Edlund
Live Melosira normannii with prominent mucilage stalks binding sand grains together in the St. Croix River, Minnesota.
8 745 33 9  Melundnorm Gv 1305 A
Credit: Mark Edlund
Girdle view showing pervalvar rows of areolae and ring of rimoportula. Collected from Jasper Lake drain, BWCAW, Cook County, Minnesota.

Original Description

  • Author
    S.Arn. ex Van Heurck 1882

Original Images

Van Heurck 1880 1881  Plxc Fig7
Van Heurck  Pl  Xc  Fig 7 Label

Cite This Page

Edlund, M., Burge, D. (2017). Melosira normannii. In Diatoms of North America. Retrieved July 19, 2024, from https://diatoms.org/species/melosira_normannii


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