• Category
  • Length Range
    14.7-33.4 µm
  • Width Range
    4.9-6.6 µm
  • Striae in 10 µm
  • Reported As
    Brachysira brebissonii (Lange-Bertalot et al. 2017 pg 186, Pl. 16: Fig 1-3)
    Brachysira brebissonii (Wojtal 2013 pg. 186-187, Pl. 16, Fig 1-3)
    Brachysira brebissonii (Kulikovskiy et al. 2010 pg 19, Pl. 49, Fig 42-49)



Valves are elliptic-lanceolate to strictly lanceolate. Valve margins are convex. Apices are non-protracted, slightly narrow, and rounded to broadly rounded. The areolae are arranged in an irregular pattern and interrupted by the hyaline area, creating a “wave-like” appearance in LM. The central area is distinct and transapically expanded to slightly rhombic. Each stria is composed of 3-4 transapically elongated areolae. The raphe is straight and with slightly expanded proximal raphe ends. Larger valves and post-initial valves have an enlarged central area that is more oval in shape. A raised marginal crest is visible using SEM.


This taxon was found in an epipelon sample from Brainard Lake Marsh, Colorado in a sample collected by Lane Allen July 11, 2021. Brachysira species grow unattached or attached to mucilage stalks. The genus is mainly benthic but can also be found in planktonic habitats.

Brachysira confusa was described in 2021 (Van de Vijver et al. 2021). It was observed in historic and recent samples collected from Scandinavian and British rivers and lakes. The type population was described from Julma Ölkky lake in Kuusamo, northeastern Finland. Lake conditions are oligo-dystrophic, electrolyte poor, and humic acid rich (Van de Vijver et al. 2021)

This taxon (reported as Brachysira brebissonii) was observed residing in freshwater habitats that have a low mineral content as well as moderately to strong acidic conditions that are due to humic acids. Additionally, the species has been documented in streams and waters on siliceous substrates. This species is a good indicator of naturally acidic conditions rather than anthropogenically acidified freshwater habitats (Lange-Bertalot et al. 2017)

It was found in the East Tatras (also reported as Brachysira brebissonii) of Poland and Slovakia in slightly acidic to slightly alkaline waters with a low specific conductivity, alkalinity, calcium concentration, and nitrate conditions. (Wojta 2013)

Home of N. amphigomphus
Credit: Lane Allen
Brainard Lake marsh, Colorado, July 2021
Brachysira confusa inital
Credit: Joy Jackson
Initial or post-initial valve with a central area that is larger and more circular in shape. Scale bar=10 µm

Original Description

Light microscopy: Valves lanceolate throughout the entire cell diminution series, with rounded, clearly convex, never rhombic-convex margins. Apices not protracted, broadly to cuneately rounded. Valve dimensions (n = 50): length 12– 45 µm, width 5.5–9.0 µm. Axial area linear, very narrow, only widening in the middle to form a very small, rhombic to occasionally rounded central area. Central area slightly transapically expanded. Raphe filiform, straight. Central raphe endings indistinct, straight. Terminal raphe endings not discernible in LM. Striae weakly radiate throughout the entire valve, 28–29 in 10 µm, composed of 3–4 clearly discernible areolae.

Scanning electron microscopy: face flat, surrounded by a clearly raised, well developed silica crest, only decreasing in height close to the apices. Apices weakly thickened. Valve face and mantle covered by a dense, irregular pattern of small spines and papillae, located on the virgae. Mantle showing one series of long, transapically elongated areolae, surrounding the entire valve without interruption, bearing some papillae on the virgae. Striae composed of 2–4, small, transapically elongated areolae, well separated by very large irregular vimines. At the apices, striae composed of one long areola. Clearly raised, almost straight, longitudinal ridges bordering the raphe branches, running from the apices to the central area, separated from the thickened apices. Central raphe endings straight, weakly expanded. Terminal raphe fissures absent, indistinct. Internally, central nodule only weakly developed with almost straight central raphe endings terminating at the edge of the nodule. Terminal raphe endings terminating on small helictoglossae. Areolae covered by individual hymenes.

  • Author
    Van de Vijver, R.L.Albert, B. Kennedy and Kusber 2021
  • Length Range
    12-45 µm
  • Width
    5.5-9.0 µm
  • Striae in 10µm

Original Images

Orignal image
Original description Brachysira

Cite This Page

Jackson, J. (2023). Brachysira confusa. In Diatoms of North America. Retrieved April 14, 2024, from https://diatoms.org/species/brachysira-confusa


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