• 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. An annulus is present at the valve center. Costae are radiate and are often not straight, rather they form a slight wavy pattern. Costae, or interfascicles, may branch in some specimens. Externally, a long spine is present at the valve margin of each costa. A single rimoportula is present on a costa near the valve face/mantle junction, replacing a spine. Numerous marginal fultoportulae are present. Central fultoportulae, however, 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 the 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). This diatom secretes long chitin fibrils from the fultoportulae. The chitin fibrils help this diatom remain buoyant in the plankton. These fibrils are clearly observable in collections of living cells.

Blooms of S. hantzschii fo. tenuis regularly occur in Pike View Reservoir, a small urban reservoir in the city limits of Colorado Springs, CO. The water treatment plant operators regularly observe this diatom, and in large numbers, the cells clog filters. Often, cell numbers increase in late fall, but the largest blooms gain momentum in February and last until mid-May. In colder months, the blooms occur under ice-cover.

Pike View Reservoir has a maximum depth of about 3 meters. The date this sample (INSTAAR 17287) was collected there were approximately 60,000 cells/mL, temperature was 8 °C, pH 9.6, dissolved oxygen 15.2 mg/L, and conductivity 1130 umhos/cm (high probably due to influx of road salt). Two weeks previous, silica concentration was 13.8 mg/L. Blooms of S. hantzschii fo. tenuis significantly raise the pH of the reservoir.

17287 Stephanodiscus hantzschii f. tenuis
Credit: Josh Logsdon, Cathleen Campbell
17287 Stephanodiscus hantzschii f. tenuis
Credit: Josh Logsdon, Cathleen Campbell

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., Edlund, M. (2016). Stephanodiscus hantzschii fo. tenuis. In Diatoms of North America. Retrieved December 05, 2022, 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.