• Category
  • Length Range
    80-155 µm
  • Width Range
    26-33 µm
  • Striae in 10 µm
    6-8 in the central valve, 7-10 at the ends



Valves are moderately to strongly dorsi-ventral, with rounded apices. The outline of valve is cymbelliform-lanceolate to broadly semi-lanceolate. The dorsal margin is strongly arched, whereas the ventral margin is slightly concave. The central portion of the ventral margin is slightly convex. The small central area is circular to oval in shape. A single, large stigma is present between the proximal raphe ends. The proximal raphe ends have distinct central pores that curve to the ventral margin. The raphe is lateral near the middle of the valve, becoming thread-like near the distal end. The terminal raphe fissures are dorsally deflected nearly 90º. Apical pore fields are present at both apices. Striae are radiate near the center of the valve, becoming parallel towards the ends. The dorsal and ventral striae in the central portion of the valve are variable in length (often 3 or more striae are half the length of the other striae). The areolae appear to be rectangular to circular in shape. Areolae adjacent to the raphe are elongated into a triangular shape. Areolae number 10-12 in 10 µm, occasionally up to 14 in 10 µm.

Note that Cymbella janischii was described as a distinct species by De Toni in 1891. Later, Patrick and Reimer (1975) considered it a variety of Cymbella mexicana. They are treated as two species in this database.


Cymbella mexicana secretes a mucilaginous stalk from either of two apical pore fields. Live cells contain one large, central golden-brown chloroplast that stretches the breadth of the valve and ~ ½ the distance to each end. For this study, C. mexicana was was found in a number of samples, including shallow water in the epilithon of Beck’s Canal, Dickinson County, Iowa (pH 6.85, 16ºC, 6.8 mg/L DO, 381 µS/cm), a boat ramp in Lazy Lagoon, Dickinson County, Iowa (pH 8.1, 16.7ºC, 6.7 mg/L DO, 449 µS/cm), and Grove Lake, Antelope County, Nebraska (pH 9, 20.7ºC, 7.1 mg/L DO, 293 µS/cm). The Iowa Lakeside Lab Herbarium contains C. mexicana specimens from epiphytic, epipsammic, and epilithic samples of East Lake Okoboji, West Lake Okoboji, Gar Lake, Beck’s Canal, and Milford Creek, all within Dickinson County, Iowa.

Other confirmed distributional records in the United States include: Montana, North Dakota, South Dakota, Wyoming, Idaho, Oregon, California (Bahls 2005), Alaska (Foged 1981), the Colorado River near Parker, Arizona (Krammer 2002), and Lake Superior (Edsall et al. 1991).

A confirmed C. mexicana fossil was reported from the Lower Klamath Lake, Oregon (Krammer 2002).

Cymbella Mexicana 20X
Credit: Mark Edlund
Cymbella mexicana, (live under 20x magnification) from Little Millers Bay, Dickinson Co., Iowa
Cymbella Mexicana 40X
Credit: Mark Edlund
Cymbella mexicana, (live under 40x magnification) from Little Millers Bay, Dickinson Co., Iowa
Becks  Canal
Credit: Lisa Allinger
Cymbella mexicana sample location at Beck’s Canal, Dickinson Co., Iowa

Original Description

Cocconema mexicanum, testula majore striata crassa lunata, ventre leviter lumido, cornubus parum elongatis obtusis, striis in 1/90"' 18 distincte et eleganter granulosis. Long. 1/18"'. Mexico.

  • Basionym
    Cocconema mexicanum
  • Author
    Ehrenb. 1844

Original Images

Cymbella mexicana orig descr

Citations & Links

Cite This Page

Johnson, B. (2011). Cymbella mexicana. In Diatoms of North America. Retrieved May 29, 2024, from https://diatoms.org/species/cymbella_mexicana


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