• Category
  • Length Range
    44.9-74.5 µm
  • Width Range
    10.2-12.5 µm
  • Striae in 10 µm



Valves are linear with parallel or slightly convex margins. The apices are barely subrostrate, so that they are just a bit narrower than the valves. The apices broadly rounded.. The axial area is narrow and widens abruptly just short of the central area. The central area is a rhombus, which is open on both sides to form a transverse fascia. The slightly curved raphe is weakly lateral and slightly complex. Proximal raphe ends are deflected to one side and terminate in small pores. Distal raphe fissures are shaped like commas or question marks. The terminal raphe fissures are surrounded by striae at the poles. The striae are strongly radiate near the valve center, becoming strongly convergent near the apices.


Pinnularia rhombarea is common in ponds and small lakes in the northern Rocky Mountains of Montana. Specimens shown on this web page are from Meadow Lake, in Missoula County. Meadow Lake has a pH of 7.5 and specific conductance of 10 µS/cm. Krammer (2000) reports P. rhombarea from northern and subarctic regions in cold oligotrophic waters with low electrolyte content.

Atlantic  Pond  Gnp 1
Credit: Loren Bahls
Atlantic Pond, Glacier National Park, Montana: home of Gomphonema americobtusatum.

Original Description

NOTE: the original description in Metzeltin and Lange-Bertalot (1998) was emended by Krammer (2000). Both the original and emended descriptions are provided here.

  • Author
    Krammer in Metzeltin and Lange-Bert. 1998
  • Length Range
    40-100 µm
  • Width
    10.5-16.0 µm
  • Striae in 10µm

Original Images

Pinnularia Rhombarea Origdesc2002
Pinnularia Rhombarea Origimag1001
Pinnularia Rhombarea Origimag2002
Pinnularia Rhombarea Origdesc1001

Cite This Page

Bahls, L. (2014). Pinnularia rhombarea. In Diatoms of North America. Retrieved August 18, 2018, from https://diatoms.org/species/pinnularia_rhombarea


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