• Category
  • Diameter
    35-120 µm



Valves disc-shaped and concentrically undulate with a convex, or concave, valve face. Valves are large and robust. Areolae are large, circular to trapezoidal to sub-hexagonal in shape, arranged in uniseriate rows in the valve center, and become fasciculate in the outer 2/3 of the valve radius. Areola foramina have a thick edge and internal domed cribra (SEM feature). Fascicles radiate from the valve center and are separated by hyaline interfascicular costae. Fascicles at the valve margins are biseriate, ending in two or more rarely three (four?) rows of areolae. Multiple fultoportulae are arranged in a loose ring in the valve center. Spines are located at the ends of every two to three costae just inside the valve face margin. A small fultoportula is positioned below each spine and above the valve margin.

Research indicates that this species is endemic, extant only in demonstrably marginal habitats, and that its morphology is highly autapomorphic (Theriot, 1992). However, the species is also found in close proximity to S. niagarae; it is highly probable that the two species are reproductively isolated and that S. reimeri occupies a unique sector of environmental space. More work is necessary to determine the origin and evolutionary histories of both S. niagarae and S. reimeri.


Stephanodiscus reimeri is thought to be restricted in distribution to West Lake Okoboji and the larger drainage system known as the “Iowa Great Lakes” (Theriot 1992, Theriot and Stoermer 1981). Live samples have been collected at Big Spirit Lake, MN and IA, and West Lake Okoboji, IA (Theriot, 1992).

In late May 2011, S. reimeri was found in Lazy Lagoon, a shallow eutrophic harbor connected to West Lake Okoboji, IA. Slides from the Iowa Lakeside Lab Herbarium include S. reimeri in planktonic, epiphytic, epipelic, and epilithic habitats of West Lake Okoboji. Stephanodiscus reimeri is considered tychoplanktonic, becoming resuspended into the water column during turnover in the spring/fall when the water column becomes unstratified. Most of the recent samples were collected using plankton nets, but other specimens have been retrieved from benthic collections after the large frustules settled on the lake bottom. Historically, abundant benthic populations are collected in West Lake Okoboji by the Iowa Lakeside Lab summer diatom class (Mark Edlund, pers. comm.).

Live  Sample 2  Ll  W  Ok  Ill2011
Credit: Phillip Woods
Live Stephanodiscus reimeri collected from Lazy Lagoon with a 35 µm mesh plankton net.
Live  Sample 3  Ll  W  Ok  Ill2011
Credit: Phillip Woods
Separated Stephanodiscus reimeri valves.
Live Sample 4  Ll  W  Ok  Ill2011
Credit: Phillip Woods
Live Stephanodiscus reimeri, girdle view.
Lazy  Lagoon  West  Lake  Okoboji
Credit: Phillip Woods
Lazy Lagoon, West Lake Okoboji, Dickinson Co., Iowa.

Original Description

Valvae disciformes, diametris 30-120 /tim visis. Area centrali convexa aut concava. Areolae in fasciculis inter costas radiantes, 8-12 in 10 /tim par- allelae ad striam. Foramina externa et cribra interna. Spinae in annulo 3-8 /tm a margine locato. Rimopor- tulae 2-11 in annulo aliquantum ulterius quam annulus spinarum locatae. Fultoportulae in annulo in area centrali et 1 fultoportula inter omnem spinam et marginem.

Valves disc shaped, with diameters 30-120 µm observed. Central area convex or concave. Areolae in fascicles between radiating costae, 8-12 in 10 /µm parallel to a stria. Foramen external and cribra internal. Spines in a ring located 3-8 /µm from the margin. From 2 to 11 labiate processes located in a ring just outside the ring of spines. Strutted processes in a ring in the central area and one strutted process between each spine and the margin.

  • Author
    E.C.Ther. and Stoermer in E.C.Ther. 1992
  • Length Range
    30-120 µm
  • Striae in 10µm
    8-12 parallel to a stria

Original Images

S Reimeri Orig Ill
S Reimeri Orig Des

Cite This Page

Woods, P. (2011). Stephanodiscus reimeri. In Diatoms of North America. Retrieved April 21, 2024, from https://diatoms.org/species/stephanodiscus_reimeri


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