• Category
  • Length Range
    260-480 µm
  • Width Range
    8-9.5 µm
  • Striae in 10 µm
  • Synonyms
    Synedra ulna f. capitata (Ehrenb.) Skabichevsky 1960
    Fragilaria capitata (Ehrenb.) Lange-Bert. 1980
  • Reported As
    Fragilaria dilatata (Krammer and Lange Bertalot 1991, pg. 476, Pl. 123, Fig 1-3)



Valves are linear and greatly elongate. The margins are nearly parallel for most of the valve, but become spathulate at the apices. That is, the apices are triangular or wedge-shaped. The apices are 9-12 µm wide at the widest point. A narrow, linear sternum is present. A central area, however, is absent. Striae are usually alternate. At the apices, striae are more radiate and less evenly spaced. The areola density is approximately 10-12 in 2.5 µm. Each valve has two rimoportulae, one at each apex.


We observed the specimens collected using a plankton net in Beck's Canal, West Lake Okoboji, Dickinson County, Iowa. We also verified this taxon on two slides of epiphytic samples in the Reimer Herbarium, one from Typha in Jemmerson Slough (Dickinson County, Iowa) collected in 1983 by R. Bovbjerg and the other from the bottom side of a yellow water lily leaf in Little Boy Creek (Cass County, Minnesota) collected in 1968 by J.D. Dodd.

Patrick and Reimer (1966) reported that this taxon is widely distributed in freshwater lakes and slow flowing rivers in North America. It was also reported from Eurasia, including Karagöl Lake in Karagöl-Sahara National Park in Turkey (Akar and Şahin 2017) and the Tryigua River in Nepal (Misra at al. 2009).

Original Description

Note there is confusion in some references with a second publication by Ehrenberg in 1836. The correct publication is Ehrenberg, C.G. (1836) Vorläufige mittheilungen über das wirkliche vorkommen fossiler infusorien und ihre grofse verbreitung In: Annalen der Physik und Chemie. Folge 2. Band 38. J.C. Poggendorf Ed., 628 pp.

IV. Das Bergmehl von Santa Fiora oder San Fiore aus KIaproth's Sammlung enthält neunzehn verschiedene Thierarten.

1) Synedra capitata n. sp. als Hauptmasse, zwischen welcher...

  • Basionym
    Synedra capitata
  • Author
    Ehrenb. 1836

Original Images

Synedra Capitata Orig Illus1
Synedra Capitata Orig Illus2
Synedra Capitata Orig Desc1

Citations & Links



  • Index Nominum Algarum
  • North American Diatom Ecological Database
    NADED ID: 245007
  • The Academy of Natural Sciences, Drexel University

Cite This Page

Bryłka, K., Lee, S. (2019). Ulnaria capitata. In Diatoms of North America. Retrieved May 29, 2024, from https://diatoms.org/species/ulnaria-capitata


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