• Category
  • Length Range
    78.5-116.5 µm
  • Width Range
    20-24 µm
  • Striae in 10 µm
  • Synonyms
    Nitzschia tryblionella Hantzsch



Valves are linear-lanceolate and gradually taper to apices that are cuneate to sometimes slightly rostrate. The raphe is keeled and eccentric, fibulae 6-8 in 10 µm. The raphe is slightly constricted at the central nodule. A longitudinal undulation is located along the apical axis of the valve. Costae at the apices are easily distinguishable (6-8 in 10 µm), while costae near the valve center may appear thinner and less pronounced (7-11 in 10 µm). Costae may appear slightly curved and non-parallel across the valve undulation. Striae are difficult to observe with light microscopy.

The original description of Tryblionella gracilis by W. Smith (1853) is valid and legitimate. The taxon was renamed Nitzschia tryblionella Hantzsch in Rabenhorst when it was transferred to Nitzschia by Hantzsch in Rabenhorst 1848-1860. The change in the specific epithet was necessary because the name N. gracilis was already occupied. When the genus Tryblionella was resurrected by Round et al. (1990), the original name Tryblionella gracilis W. Smith 1853 was again recognized as the valid and legitimate name of this taxon.


Tryblionella gracilis was found in an epiphytic sample taken in Beck's Canal, Dickinson County, Iowa, a site with slightly basic water (pH 8.05). Additionally, T. gracilis specimens in the Reimer Herbarium were collected in a benthic sample from Lazy Lagoon, Dickinson County, Iowa. Tryblionella gracilis is found in a variety of habitats: coastal, brackish, and fresh water. (Hofmann et al. 2011).

Usgs  Tryblionella Gracilis
Credit: USGS BioData
Distribution of Tryblionella gracilis in rivers of the continental U.S. based on the National Water Quality Assessment program. Retrieved 10 June 2016.

Original Description

  1. Tryblionella gracilis, n. sp. F.V. linear, attenuate towards the extremitics; V. linear acuminate ; canaliculi parallel, extending to the central line, 10 to 12 in.001” ; alae distinct. Length .0023” to 0075”. v.v. Fresh and brackish water. Near Lewes, Dec. 1850, and Oct. 1852, W. Sm. Plate X. 75. Frustule with endochrome, Frontispiece, fig. LXXV.
  • Author
    W.Sm. 1853
  • Length Range
    23-75 µm

Original Images

Tryblionella Gracilis Orig Ill
Tryblionella Gracilis Orig Desc

EMAP Assessment

EMAP Distribution

Tryblionella Gracilis  Smith 40
Map 40

Response Plots

Tryblionella Gracilis  Smith

Cite This Page

Lister, J. (2016). Tryblionella gracilis. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/tryblionella_gracilis


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