• Category
  • Length Range
    16-20 µm
  • Width Range
    3.1-3.8 µm
  • Striae in 10 µm



Valves are linear, with an abrupt tapering to small, knob-like apices. An indistinct longitudinal fold extends the length of the valve. The canal raphe is excentric. Fibulae are indistinct and aligned with the striae. Striae are parallel and composed of distinct, squarish areolae.

The longitudinal fold suggests that this diatom should be considered for transfer to the genus Tryblionella.

Krammer and Lange-Bertalot (1988, p. 47) describe the challenges of recognizing differences in this group of small Tryblionella-like Nitzschia species that includes N. angustatula Lange-Bert., N. compressa (Bailey) Boyer, and N. compressa var. vexans (Grunow) Lange-Bert. Indeed, N. angustatula may prove to be conspecific, as the dimensions (L = 13-24 µm, W = 4 µm, S = 16-20 in 10 µm) overlap between the two taxa.

Note that Reimer (1966) described the taxon N. silicula var. commutata based on a single specimen. The specimen holotype is displayed on this page (above) and was identified on ANSP 44258a (not 44268a as indicated in Reimer’s publication). This taxon is very similar in morphology, and we consider it here within N. siliqua. Reimer (1966, pp. 9-10) also suggests comparison with N. subpunctata Cholnoky 1960.


Images on this page are from collections in South Dakota and South Carolina. This taxon has also been reported from the EPA Western EMAP survey, and from the USGS regional survey of California.

Original Description

Nitzschia siliqua n. sp.

This species belongs to the group of Nitzschiae which are similar to N. amphibia GRUNOW (cf. HUSTEDT, 1930: 414, F. 793). I have, however, been unable to associate it with N. amphibia or any other species of the group known to me. The valve is linear with parallel sides and cuneate poles which are protracted into slightly capitate ends, 22-23 μ long, and about 3 μ wide. The keel is not easily distinguishable from the rest of the structure and the carinal pores are either not visible or are of the same number as the transapical striae. The transapical striae are coarse and easily seen, 16-18 in 10 μ. Longitudinal costae are visible and straight, about 27 in 10 μ. -- Fig. 62. -- Vaal 402.

Valvae lineares, marginibus parallelis, apicibus cuneato attenuatis, protractis, levissime capitatis, 22-23 μ longae, circiter 3 μ latae. Carina non bene visibilis, pori carinales indistinctae, probabiliter striis aequidistantes. Striae transapicales crassae, distinctissimae, 16-18 in 10 μ. Costae longitudinales distinctae, directae, circiter 27 in 10 μ, itaque striae ex punctis distinctis compositae esse conspiciuntur.

Habitat in decurso lacus artificiali putei uni carbonis Grootvlei dicti inter pagos Balfour et Villiers in Africa Meridionale.

Typus: praeparatum No. Vaal 402 in collectione C. S. I. R., Grahamstown.

Iconotypus: figura nostra No. 62.

  • Author
    R.E.M.Archibald 1966
  • Length Range
    22-23 µm
  • Width
    3 µm
  • Striae in 10µm

Original Images

N Siliquaorigfig
N Siliquaorigdesc

Cite This Page

Polaskey, M. (2020). Nitzschia siliqua. In Diatoms of North America. Retrieved December 07, 2021, from https://diatoms.org/species/nitzschia_siliqua


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