• Category
  • Length Range
    71-124 µm
  • Width Range
    14-16.5 µm
  • Striae in 10 µm
  • Synonyms
    Navicula macilenta Ehrenb. 1837
    Navicula oblonga var. macilenta (Ehrenb.) Schumann 1867
    Navicula oblonga var. macilenta (Ehrenb.) Perag. 1903
  • Reported As
    Pinnularia subgibba var. hustedtii (Krammer 1992)



Valves are linear-lanceolate. Specimens at the larger end of the size range have a slightly gibbous central area. Apices are broadly rounded and in larger specimens, slightly subcapitate. The axial area is broad, about 1/4-1/2 the width of the valve. The central area is wide, irregular, and rhombic. A small, asymmetrical transverse fascia is usually present. The central area has four large markings, although they are not always visible in LM. The raphe is broadly lateral with terminal fissures having the shape of a question mark. Striae are radiate in the center, becoming convergent toward the ends.

The iconotype illustration (Ehrenberg 1837) shows a diatom with linear valves, straight margins, and a narrow axial area, a concept followed by Krammer (1992).

Later, Reichardt (1995) examined the type material from Cayenne and concluded that P. subgibba Krammer 1992 is a subjective synonym of P. macilenta. We note, however, that specimens from type material illustrated by Reichardt (1995) are more linear and narrow (7-13 μm).

In a slightly different interpretation, Krammer (2000) stated that only the variety P. subgibba var. hustedtii Krammer 1992 is conspecific with P. macilenta. Our specimens are most similar to those presented as P. macilenta in Krammer (2000), although they differ by being are wider and more lanceolate.


Images shown here are from sediments of a lake in New Jersey. The species was described from Cayenne, French Guiana (Ehrenberg 1837), so it likely has a moderately wide geographic distribution.

Original Description

  • Basionym
    Navicula macilenta
  • Author
    Ehrenb. 1837

Original Images

Pinn macilenta org img 01
Pinn macilenta org img 02
Pinn macilenta org img 03
Pinn macilenta org descrp

Cite This Page

Aycock, L. (2022). Pinnularia macilenta. In Diatoms of North America. Retrieved June 19, 2024, from https://diatoms.org/species/pinnularia-macilenta


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