• Category
  • Length Range
    60.5-251.6 µm
  • Width Range
    4.2-4.9 µm
  • Striae in 10 µm
    11-12
  • Synonyms
    Synedra affinis var. arcus (Kütz.) Grunow in Van Heurck 1881
    Synedra goulardii var. acus (Kütz.) Freng. 1925
    Fragilaria ulna var. acus (Kützing) Lange-Bert. 1980

Identification

Description

Valves are narrow and lanceolate. The apices are protracted, narrowly attenuate, and mostly sub-rostrate to sub-capitate. The sternum is lanceolate, distinguishable under LM, and ranges in shape from linear to slightly expanded near the central area. The parallel striae are coarse, mostly occurring opposite or occasionally alternate. Rimoportula are present at the apices. Striae along the margin of central area may be reduced or absent, with ghost striae often present.

There has been much confusion regarding the identity of this taxon that can be attributed to the lack of original type material, line drawings and a suite of similar needle-like taxa. Lange-Bertalot and Ulrich (2014) designated a neotype for Ulnaria acus based on Kützing material from Falaise, France (no. 401, BM 18305).

Ulnaria acus as presented on this page increases the length range reported by Lange-Bertalot and Ulrich (2014). We do not find North American specimens that are lacking a central area with ghost striae, as in the neotype population (Lange-Bertalot and Ulrich 2014; Pl. 25, Figs 2, 3). Also note that Lange-Bertalot and Ulrich (2014) used Fragilaria grunowii to describe larger specimens that have very narrowly attenuate apices. Our specimens of U. acus overlap in length range with F. grunowii, but we consider U. acus to have attenuate apices.

Autecology

Ulnaria acus was sampled from a biofilm on a submerged buoy at the outlet of Beck’s Canal to West Okoboji Lake (Dickinson County, Iowa) and in epilithic biofilms submerged near the shore of the Missouri River off Riverside Park, Yankton (Yankton County, South Dakota). Ulnaria acus specimens from the Charlie C. Reimer Herbarium (Iowa Lakeside Laboratory, Milford, Iowa) were found in epilithic and epiphytic habitats (macrophytic algae and Typha stalk) and on the bottom of a small pool in Silver Lake Fen (Dickinson and Hamilton County, Iowa).

Patrick and Reimer (1966) observed this taxon (as Synedra acus) widely distributed across the United States in circumneutral rivers with moderate conductivity and hardness. Ulnaria acus is found in epilithic and epiphytic biofilms in moderately alkaline, oligosaprobic, and eutrophic freshwater streams and lakes (Lange-Bertalot and Ulrich 2014).

Ulnaria Acus Plate Modified
Size diminution series of U. acus from West Lake Okoboji
Ulacus L48
Credit: USGS BioData
Distribution of Ulnaria acus in rivers of the continental U.S. based on the National Water Quality Assessment program. Retrieved 02 December 2016.
Ulacus Hawaii
Credit: USGS BioData
Distribution of Ulnaria acus in rivers of Hawaii based on the National Water Quality Assessment program. Retrieved 02 December 2016.
Ulacus Alaska
Credit: USGS BioData
Distribution of Ulnaria acus in rivers Alaska based on the National Water Quality Assessment program. Retrieved 02 December 2016.

Original Description

  • Basionym
    Synedra acus
  • Author
    Kütz. 1844

Original Images

Ulnaria Acus Pic
Ulnaria Acus Des1

Cite This Page

Burge, D., Tunno, I., Edlund, M. (2016). Ulnaria acus. In Diatoms of North America. Retrieved December 13, 2019, from https://diatoms.org/species/ulnaria_acus

Responses

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