• Category
  • Length Range
    32-67 µm
  • Width Range
    3-4 µm
  • Striae in 10 µm
    12-14 in the center valve, 14-15 at the ends
  • Synonyms
    Neofragilaria acidobiontica (Charles) D.M.Williams and Round



Valves are linear with rostrate ends. Striae are uniseriate and parallel throughout the valve. A narrow, hyaline interruption of the striae is present submarginally on the same side of the valve as the rimoportula (best seen in SEM). In girdle view, valves are rectangular and 4.3-6.1 µm in depth. Frustules often form band-shaped colonies, joined by marginal linking spines.


Charles (1986) named F. acidobiontica given the characteristic nature of it's occurrence in low pH lakes, Camburn and Charles (2000) further corroborate the previous findings with occurrences from lakes with 5.5 ph or lower. Fragilariforma acidobiontica is often found occurring with other acidophiles such as Oxyneis, Semiorbis, and Actinella punctata.

The known distribution of F. acidobiontica is currently limited to surficial sediments of low alkalinity lakes in the Adirondacks of New England, USA and Ontario, Canada (Camburn and Charles 2000).

Original Description

Frustules narrowly rectangular in girdle view, 2-7µm along the pervalvar axis forming flat, ribbon-like colonies. Valve linear to linear-lanceolate with small, slightly asymmetrical, rostrate to slightly capitate apices. Length 22-86µm, breadth of valve 3.0-4.5µm. Valves held together by linking-spines present along the margin of the valve face. Spines lobate at apices, becoming bilobate to more complex toward mid-valve region. Axial area and central area lacking; striae continuous across middle of valve face. Striae interrupted along one margin, forming a narrow discontinuous line along the length of the valve, often indiscernible with the light microscope. Striae 10-14 in 10µm on valve face and valve mantle, denser toward ends, parallel throughout. Striae composed of punch, about 50 puncta in 10 µm. Labiate process at apex, offset toward side of valve with interrupted striae. Acidobiontic, occurs primarily in dilute waters with pH less than 5.5. Found in surface sediments of lakes in the Adirondack Park, New York and New Hampshire, USA, and Ontario, Canada.

  • Basionym
    Fragilaria acidobiontica
  • Author
    Charles 1986
  • Length Range
    22-86 µm
  • Width
    3-4.5 µm
  • Striae in 10µm

Original Images

Fracidobiontica Original Image
Fragilaria acidobiontica orig illus
Fracidobiontic Original Description

Cite This Page

Burge, D. (2015). Fragilariforma acidobiontica. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/fragilaforma_acidobiontica


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