• Category
  • Length Range
    101-162 µm
  • Width Range
    22.5-26.7 µm
  • Striae in 10 µm
    transverse striae 11.9-14.3; longitudinal striae 20.0-23.8
  • Reported As
    Navicula halophila var. maior (Héribaud (in Boyer 1927))



There are three valve types found for this taxon: vegetative, "heribaudii", and craticula forms. The three forms are produced as a cellular strategy for surviving inimical conditions such as desiccation (Schmid 1979). Two craticula are formed within the vegetative frustule and subsequently the "heribaudii" cell is formed within the craticula. The heribaudii cell usually has different ornamentation compared to vegetative cell.

Vegetative valves are fusiform-lanceolate, with acutely rounded (shorter valves) to pointed apices (longer valves), never protracted. The axial area is narrow and strongly silicified. The central area is only slightly expanded. Raphe filiform to slightly lateral. Proximal raphe ends curve slightly to same side of valve and terminate in a small hook. Terminal raphe fissures are sickle-shaped and hooked toward the same side of the valve. Slit-like and apically elongate areolae arranged in both transapical and longitudinal striae, with transapical striae more prominent. Transapical striae are parallel throughout the valve, becoming slightly convergent near the apices. Longitudinal striae arranged in slightly wavy rows.

"Heribaudii" forms have similar shape, size, and raphe features as vegetative valves. Slit-like and apically elongate areolae (21 in 10 µm) are arranged only in transapical striae. Transapical striae radiate (1.9-11.6 in 10 µm) becoming parallel to convergent only at the valve ends.

The craticula forms have similar shape and size as the vegetative valves, but are very heavily silicified and comprise a central sternum, parallel transapical ribs (1.5-1.8/10 µm), a thick margin, and circular to oval to quadrilateral openings.


Craticula coloradensis is known only from its type locality, Radford Peak, Colorado. Associated taxa include Hantzschia amphioxys.

Original Description

Valve linear-lanceolate, gradually tapering to acute, rounded ends. Axial area narrow, distinct. Central area not clearly differentiated from the axial area. Striae parallel throughout the valve; punctate, the puncta forming longitudinal and transverse lines. Transverse lines, 15 in 10 µ. Longitudinal lines, 24-28 in 10 µ. Length, 127-146 µ. Breadth, 23-29 µ.

  • Basionym
    Navicula cuspidata var. obtusa
  • Author
    R.M.Patrick (nom. illegit.) 1966
  • Length Range
    127-146 µm
  • Width
    23-29 µm
  • Striae in 10µm
    14-17 transverse, 24-28 longitudinal

Original Images

N Halophila Obtusa Orig Illus
N Cuspidata Obtusa Orig Des


Jan 25, 2017 - Transfer to Craticula

The basionym of this taxon, Navicula cuspidata var. obtusa R.M.Patrick nom. illegit. (1966) is a later homonym of Navicula cuspidata var. obtusa Grunow (1860). Edlund et al. (2017) formally proposed the transfer of Navicula cuspidata var. obtusa R.M.Patrick to Craticula with a new name and with species status as Craticula coloradensis Edlund, D.R.L.Burge & S.A.Spaulding. From May 2015 until January 2017, this taxon appeared on this site as Navicula cuspidata var. obtusa R.M.Patrick. - M.B. Edlund

Cite This Page

Edlund, M. (2017). Craticula coloradensis. In Diatoms of North America. Retrieved June 24, 2018, from https://diatoms.org/species/navicula_cuspidata_obtusa


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