• Category
  • Diameter
    30-81 µm
  • Width Range
    28-47 µm
  • Striae in 10 µm



Barrel-shaped frustules are heavily silicified. The valve faces are flat and joined together to form long, filamentous colonies. In girdle view, the mantles are unevenly thickened internally, creating an undulating appearance. A ring of evenly-spaced rimoportulae encircles the mantle, near the valve edge. Several rimoportulae are also present on the surface of the valve. Striae on the valve face are dichotomously branched and radiate from a hyaline central area. Areolae number 13-19 in 10 µm.


Melosira undulata is reported to be a soil diatom, but is also found in oligotrophic lakes (Krammer & Lange-Bertalot 1991). The population of M. undulata described here was collected on 13 June 2012 at Giant Springs State Park on the Missouri River near Great Falls, Montana. Giant Springs is one of the largest freshwater springs in the world and discharges at a rate of 4.37 cubic meters per second. Water in the springs originates in the Madison limestone formation of the Little Belt Mountains, about 75 miles distant. At the point of discharge, water in the springs measures a constant 12.2 degrees C. The sample containing M. undulata was collected from rocks and concrete that line the spring pool. On the day of collection, water temperature in the pool measured 14.6 degrees C, pH measured 7.50, and specific conductance measured 580 µS/cm. A common diatom associate in this sample was another robust, colony-forming centric: Ellerbeckia arenaria.

Meloundulata Plastids 400 X
Credit: Loren Bahls
A broken frustule of Melosira undulata with intact cytoplasm containing numerous discoid plastids. 400X
Giant Springs  Mdfwp
Credit: Montana Department of Fish, Wildlife & Parks
Giant Springs near Great Falls in Cascade County, Montana: Type locality of Cymbella fontinalis

Original Description

  • Basionym
    Gallionella undulata
  • Author
    Ehrenb. 1840

Cite This Page

Bahls, L. (2012). Melosira undulata. In Diatoms of North America. Retrieved April 21, 2024, from https://diatoms.org/species/melosira_undulata


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