• Category
  • Length Range
    19.0-38.6 µm
  • Width Range
    4.0-5.7 µm
  • Striae in 10 µm
    32-34, more closely spaced towards the apices



Valves are lanceolate to linear-lanceolate and sometimes heteropolar. Apices are narrowly rounded or sub-rostrate to weakly subcapitate. The axial area is narrow. The central area is a narrow ellipse oriented lengthwise along the apical axis. The raphe is straight. Proximal raphe ends are weakly expanded and relatively distant from one another. Striae are radiate. Areolae are transapically elliptic to bacilliform. Areolae are irregularly spaced, creating a pattern of undulating longitudinal lines.


The images of B. ocalanensis on this website are from Johns Lake in Glacier National Park, Montana (photo below). On the collection date, the pH of Johns Lake was 7.24 and specific conductance measured 30 µS/cm. It has also been recorded from other lakes in Glacier National Park. This species was described from Wildcat Lake on the Ocala National Forest in Florida, which had a pH of 4.83 and a specific conductance of 52.4 µS/cm (Shayler & Siver 2004). It may seem odd that a species described from Florida would appear in the mountains of northwest Montana, but consider that B. arctoborealis, a species described from the Canadian Arctic, has also been reported from the Cascade Mountains of Washington, from Florida, and even from Borneo!

Johns  Lake  Gnp  Hikespeak Com
Credit: Hikespeak.com
Johns Lake, Glacier National Park, Montana: home of A. rostellata

Original Description

  • Author
    Shayler and Siver 2004
  • Length Range
    21.5-35.5 µm
  • Width
    4-6 µm
  • Striae in 10µm

Original Images

Brachysira ocalanensis orig illus
Brachysira ocalanensis orig descr

Cite This Page

Bahls, L. (2014). Brachysira ocalanensis. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/brachysira_microcephala_morphotype_1


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