• Category
  • Diameter
    15.5-19 µm
  • Striae in 10 µm
    5.7-7.5 based on circumferential density



The valve flat is flat and lightly silicified. Areolae are fine, occurring 26-28 in 10 µm, arranged in multiseriate fascicles. The fascicles number 5.7- 7.5 in 10 µm based on circumferential density. Areolae in the valve center are always arranged in an annulus. Fascicles are often not straight, showing a slight wavy pattern, and branching in some specimens. Long spines occur at each interfascicle. A single rimoportula is present on an interfascicle, near the valve face/mantle junction, replacing a spine. Central fultoportulae are absent.

This taxon is considered to be an environmental forma, favored in particular conditions (Anderson 1990). Stephanodiscus hantzschii and S. hantzschii fo. tenuis often co-occur, with forma having a higher total phosphorus optimum than the nominate variety (Reavie and Kireta 2015). Others have suggested the forma is indicative of silica limitation (Stoermer et al. 1979). Heterovalvar frustules may be found, further supporting the conclusion that the environment shapes the morphology of this taxon (Anderson 1990).


Stephanodiscus hantzschii fo. tenuis was reported from nearshore and high energy zones of lakes Erie and Ontario (Reavie and Kireta 2015). It is considered characteristic of eutrophic lakes, particularly in higher total phosphorus concentrations (Reavie and Kireta 2015), and under silica limitation (Stoermer et al. 1979).

Original Description

  1. Stephanodiscus tenuis nov. spec. Schalen fast flach, nur wenig konzentrisch gewellt, dünnwandig, 8-28 µ ins Durchmesser, durch zarte radiale Ripen in mehr oder weniger zahlreiche Sektoren geteilt, die aus breiter Basis gegen das Zentrum allmählich schmäler werden. Zwischenräume zart areoliert. Areolenreihen am Rande etwa 4-5 in jedem Bündel. Vor den radialen Rippen innerhalb des Schalenrandes lange Randdornen.
  • Basionym
    Stephanodiscus tenuis
  • Author
    Hust. 1939
  • Length Range
    8-28 µm

Original Images

Sttennuis Orimage
Sttennuis Ordesc

Cite This Page

Burge, D, and Edlund, M. (2016). Stephanodiscus hantzschii fo. tenuis. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/stephanodiscus_hantzschii_f._tenuis


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Stephanodiscus hantzschii fo. tenuis 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.