• Category
  • Length Range
    95-157 µm
  • Width Range
    24-36 µm
  • Striae in 10 µm
    12-14 transverse, 24-26 longitudinal
  • Synonyms
    Navicula cuspidata (Kütz.) Kütz. 1844
    Navicula cuspidata var. heribaudii Perag. in Hérib. 1893



Valves are rhombic-lanceolate and widest at the center of the valve before tapering to narrow apices. Striae are parallel and equidistant throughout the entire valve, with thin transapical costae intersecting perpendicular to the longitudinal striae forming an orthostichous pattern. Striae are composed of small, elliptic areolae, approximately 12-14 in 10 µm in the transverse direction and 24-26 in 10 µm longitudinally. The axial area is narrow with a slightly widened central area with slightly concave margins. The raphe is filiform. The proximal raphe ends are expanded and either straight, or slightly hooked in the same direction. The distal raphe ends form hooks, deflected in the same direction.

This species is polymorphic and forms modified valves termed craticulae and heribaudii valves, as in other species within the genus Craticula. The polymorphic valves are formed as the result of increases in salinity. Craticular valves possess a central rib with plates that extend transapically across the valve, but the ribs lack a consistent definite shape or pattern. Craticula valves lack a raphe system. Heribaudii valves have radial, punctate striae that appear to retain an equal distance between striae. Unlike the craticula valves, heribaudii valves possess a simple raphe system similar to vegetative valves.

Patrick and Reimer (1966, plate 43, fig 10) illustrate a capitate form within the species Craticula cuspidata. However, Lange-Bertalot (2001) note that this smaller morph is incorrectly included within C. cuspidata, and should be recognized as the distinct species C. ambigua (Ehrenberg) Mann 1990. This web flora also recognizes C. ambigua. Note, however, that many previous reports of C. cuspidata in North America include C. ambigua.


This taxon is found in various freshwater benthic habitats, and can often be found in epiphytic, epipelic, and epilithic substrata. It is tolerant of a range of water quality conditions, but sudden environmental changes in ion balance or salinity may cause the formation of resting spores and the morphologically differing “craticula” and “heribaudii” valves (Schmid 1979; Mann and Stickle 1991). Populations have been reported throughout the United States.

This taxon has been shown to reduce nitrate/nitrite reduction to ammonium (Merz et al. 2020). Cells are able to migrate vertically in sediments, on a diel basis. Cells rapidly accumulated NO3 in surface sediments then descended to deeper, anoxic sediments for most of the day. Nitrate/nitrite reduction to ammonium was shown to be the primary metabolic path for this diatom in the absense of light.

C Cuspidata Live 1
Credit: L. Fuelling
Live Craticula cuspidata cell with chloroplasts appressed to the valve mantle.
C Cuspidata Live 2
Credit: L. Fuelling
Live C. cuspidata cell at an oblique angle, displaying small, spherical lipids and two larger volutin granules.
C Cuspidata Live 3
Credit: L. Fuelling
Live Craticula cuspidata cell with two distinctive volutin granules, chloroplasts appressed to the valve mantle. The simple raphe system is also visible.
Diatom  Camp 171
Credit: L. Fuelling
Open waters of Beck’s Canal, Dickinson Co., Iowa, bordered by epiphytic and epipelic habitats where populations of C. cuspidata are commonly found.
Diatom  Camp 172
Credit: L. Fuelling
Craticula cuspidata inhabits various benthic substrata, and grows epiphytically on duckweed (Lemna spp.).

Original Description

  • Basionym
    Frustulia cuspidata
  • Author
    Kütz. 1833

Original Images

Frustulia cuspidata orig illus
Frustulia cuspidata orig illus

Citations & Links


Cite This Page

Fuelling, L., LaLiberte, G. (2011). Craticula cuspidata. In Diatoms of North America. Retrieved May 18, 2024, from https://diatoms.org/species/craticula_cuspidata


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