Diatoms of North AmericaDiatoms of North America

Aulacoseira pseudoamericana

(Camburn) Siver and Kling 1997

Aulacoseira pseudoamericana guide
  • Category
    Centric
  • Diameter
    5.7-10.5 µm
  • Width Range
    3.3-5.3 µm
  • Striae in 10 µm
    18-24 on valve margin
  • Synonyms
    Melosira pseudoamericana Camburn 1989

Identification

Aulacoseira pseudoamericana LM7 Aulacoseira pseudoamericana LM1 Aulacoseira pseudoamericana LM4 Aulacoseira pseudoamericana LM6 Aulacoseira pseudoamericana LM2 Aulacoseira pseudoamericana LM5 Aulacoseira pseudoamericana LM3
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Aulacoseira pseudoamericana SEM

Description

Frustules are cylindrical, joined in chains by linking spines. The mantle has straight sides, but the sulcus may be constricted, so that the frustules appear pinched into a bow-tie like shape. The mantle is unornamented, except for grooves near the face-mantle junction where spines from adjoining valves attach. This feature is not always resolvable in LM. The valve face is flat, with up to three irregular rows of small, scattered areolae on the margin.

The spines are conspicuous and robustly spatulate - or narrowly apiculate. The spines are positioned at the face-mantle junction of each valve. Spines may be several microns long. Spines number between 10-14 in 10 µm, with the longest spines extending 2 µm from the valve face.

Long chains of frustules are common and the colonies can often curve due to the length of the spines. 

Aulacoseira pseudoamericana and A. perglabra have been confused or even combined in some studies (Siver and Kling 1997). While both taxa have robust spines that are visible in LM, but A. perglabra has a distinct buttress that extends from the base of the spines deep into the mantle. The diameter and height of both species can overlap, so the two can be distinguished by observing the ornamentation of the mantle and valve face. SEM is not necessary to separate the two species, but small valves can be difficult to differentiate in LM.


Autecology

This taxon has been reported from surface sediments of lakes in northern Michigan, Wisconsin, and Minnesota (Camburn and Kingston 1986). Those authors observed that species of Aulacoseira reflected trophic status of lakes in Michigan. Aulacoseira nygaardii, A. perglabra and A. pseudoamericana were common in bottom sediments, but absent in the top sediments deposited under conditions of greater human impact. These taxa were replaced by other diatoms, including A. ambigua.

Specimens shown on this page here were found in surface sediment samples taken from Wildcat Lake in Lake County (1982) and Lake Artillery in Hillsborough County (2003), Florida. Both of these lakes are historically acidic and have not exceeded a pH of 6.4 according to the Florida Water Atlas, but they differ in terms of color, depth, and numeric nutrient criteria, though both systems are relatively shallow. The type locality, Cusino Lake in Michigan, has historically been a shallow acidic lake according to the EPA, and Camburn notes that a large population of A. pseudoamericana was recorded from a small bog-lake called Wenzel's Pond in Wisconsin. This suggests this taxa is likely acidophilic and found in generally shallow systems with acidic to neutral pH. 

The individuals seen in Wildcat Lake and Lake Artillery were found coexisting with Eunotia spp., A. herzogii, and Tabellaria spp.

Original Description

Frustules rectangular in girdle view, valves slightly rounded at the mantle. Valve disc-shaped and slightly convex, (5.5) 9.0—14.0 (16.5) µm in diameter. Pervalvar axis usually less than diameter except in small specimens. Valve mantle unornamented. Periphery of valve face ornamented with a narrow (1.0—1.5 µm) band of puncta. Ornamentation composed of 2 irregularly concentric rows of puncta, a partial third row often occurs. No relationship exists between the placement of these rows as they are not consistently radially or tangentially arranged. Puncta 18—22 in 10 µm near the valve margin. The remaining valve face is unornamented. A row of spines occurs around the circumference of the valve face, spines 10—12 in 10 µm. Spines ca. 1.5—2.0 µm in length.

Habitat: Occurs in surface sediments from 12 lakes in northern Michigan, Wisconsin and Minnesota.

Holotype: A.-G.C. #54238. In general diatom collection, Academy of Natural Sciences of Philadelphia.

Type Locality: U.S.A., Michigan, Schoolcraft County, Cusino Lake, 47N16W24, 46º 27’ 16” , 86º 15’ 30”, Surface Sediment (0-1cm) from 11 m, June 24, 1983.

  • Basionym
    Melosira pseudoamericana
  • Author
    Camburn 1986
  • Length Range
    (5.5) 9.0-14.0 (16.5) µm
  • Width
    Less than diameter µm
  • Striae in 10µm
    18-22 on face near valve margin

Original Images

Ps am orig photos

Cite This Page

Rytlewski, I., Burge, D., Whitmore, T. (2024). Aulacoseira pseudoamericana. In Diatoms of North America. Retrieved June 20, 2025, from https://diatoms.org/species/319604/aulacoseira-pseudoamericana

Responses

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