Pinnularia formica | Species - Diatoms of North America

Category

Symmetric Biraphid
Length Range

84-162 µm
Width Range

12-18 µm
Striae in 10 µm

8-9

Synonyms

Navicula formica Ehrenb. 1843
Pinnularia nodosa var. formica (Ehrenb.) Cleve

Contributor

Meredith Tyree Polaskey, Hayden Ripple - Jan 2018
Reviewer

Sarah Spaulding - Mar 2018

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Identification

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Description

Valves with a large expanded central valve and distinctly capitate apices. The center expansion of the valve is longitudinally elliptic. The striae are constrained to the margin of the valve face, creating a large axial area, up to roughly 2/3 of the valve face. Striae are weakly radiate to parallel near the central area, transitioning to convergent at the apices. Striae are longer near the apices. The raphe is lateral. Proximal raphe ends are deflected unilaterally and terminate in a teardrop shape. Within a frustule, the raphe of each valve are offset to one another. The distal ends of the raphe are strongly deflected toward the same side. Distal ends of the raphe terminate in a "question mark" shape.

Autecology

Pinnularia formica was originally described from Maine (Ehrenberg 1843). Since its first record, this taxon has been found in lentic and lotic freshwater systems in the northeastern US, including in Virginia (Matthews, see live image), North Carolina, South Carolina, Georgia (USGS BioData) and - Texas (USGS BioData).

Size Range, µm3

10001-100000
Motility

Highly motile
Attachment

Unattached
Habitat

Benthic
Colony

Solitary
Occurrence

Rare
Waterbody

Inland Rivers Lakes
Learn more about this

Credit: Robin Matthews, Professor Emeritus, Western Washington University

36.6209155, -76.5246325 Railroad Ditch, which us a tributary to Lake Drummond in the Great Dismal Swamp, Virginia

Credit: USGS Biodata

Pinnularia formica occurence in river surveys by USGS.

Credit: www.CT.gov - Connecticut Department of Energy and Environmental Protection.

Halls Pond, Maine - the type locality of P. formica.

Original Description

144 N. formica, testula a dorso anguste linearies quater constricta, articulis spuriis oblongis. Maine A, nec Bridgwater.

Basionym

Navicula formica
Author

Ehrenb. 1843

Original Images

Citations & Links

Citations

Cite This Page

Polaskey, M., Ripple, H. (2018). Pinnularia formica. In Diatoms of North America. Retrieved December 08, 2025, from https://diatoms.org/species/84110/pinnularia_formica

Responses

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