• Category
  • Length Range
    15.7-40 µm
  • Width Range
    8.7-22 µm
  • Striae in 10 µm
    Raphe valve 15-18.5, rapheless valve 7–12



Valves are elliptic to slightly elongate-elliptic.

The raphe valve has a narrow axial area, a small circular central area and straight filiform raphe. Striae are parallel at the center, radiate and slightly curved toward the apices. In some specimens, the central striae are slightly separated by wider virga on one side of the valve. Striae are interrupted by a hyaline submarginal ring with uneven margins and a bumpy appearance. Areolae are well distinguished under LM, and number 18-24 in 10 µm.

The center of the rapheless valve has parallel, straight striae, which become radiate and very slightly curved near the apicies. The sternum is narrow and linear. Areolae are coarse and transapically elongated. Areolae vary in size and structure, as they may be lineolate, rectangular, oblong, or oval.


This diatom was described from Hat Creek (40.851099, −121.5364), located in Lassen National Forest in the Southern Cascade Mountains, California. It inhabits mountain streams in California with pH 5.9–9.3, salinity 0–0.1 ppt, water temperature 6.2–16.3°C, conductivity 59–138.7 μS cm1, total nitrogen below 0.17 mg L1, total phosphorus below 0.08 mg L1, and dissolved organic carbon below 1.15 L1.

Original Description

Cocconeis cascadensis Stancheva, sp. nov. (Figs 1–33)

Description.Valves large, elliptical to slightly elongate-elliptical with rounded apices (Figs 1–12). SV striae parallel and straight at the centre, radiate and very slightly curved towards the apices; sternum narrow, linear (Figs 1,2, 5–7). Striae in the middle portion of the valve often separated by wider virgae on one side of the valve (Figs 1, 5,6, 10). Areolae coarse, transapically elongated, of different sizes and variable appearance, i.e., lineolate, rectangular, oblong or oval. The marginal areolae close to the mantle narrower and lineolate (Figs 5–7).

RV with straight, filiform raphe, narrow axial area and small elliptical central area (Figs 3, 4, 8, 11, 12). Striae parallel and straight at the centre, radiate and slightly curved towards the apices, with small and round areolae clearly distinguishable with LM, the central striae some-times slightly separated by wider virgae on one side of thevalve (Fig. 8). Striae interrupted near the valve margin by a thickened hyaline area with uneven margins and bumpy appearance (Figs 3, 4, 12).

In SEM, SV striae uniseriate. Areolae externally depressed, slit-like lumen enclosed in large crater-like structure (Figs 19, 20, 22); crater-like depressions variable in size, strongly developed in the central part of valve face (Figs 13–19), and weakly developed along the sternum and near the mantle (Figs 17, 18). Internally, areolae closed by hymenes with long, regular and oblique slits (Figs 21, 24). Several small pores visible between striae in many valves, both externally (Figs 13, 14, 17, 18, 20) and internally (Fig. 23). In SEM, RV striae uniseriate. Internally, areolae closed by hymenes with a marginal row of linear slits (Figs 32, 33). Striae interrupted by a slightly raised sub-marginal area separating a single row of marginal areolae (Figs 25–27). Submarginal area with irregular margins, internally bearing apically elongated bumps (Figs 28, 29). Raphe filiform, internally with proximal raphe fissures deflected on opposite sides and distal raphe endings with visible helictoglossae (Figs 25, 26). Externally, proximal raphe ends are drop-shaped, and distal ends are straight, distant from the margin. RV valvocopula margin with indentations (Fig. 30), open at one pole (Fig. 31).

Dimensions. Length: 15.7–40 μm; width: 8.7–22 μm;striae: SV: 7–12 in 10 μm, RV: 15–18.5 in 10 μm; areolae: SV: 3–7 per stria to a single areola near the apices, RV:18–24 in 10 μm.

Holotype. Slide GC 65323, The Academy of Natural Sciences Philadelphia Diatom Herbarium, USA. Holotype specimen is illustrated on Fig. 2. Isotype. Slide GC 65324 and cleaned material GCM5762, both from Montgomery Creek, The Academy of Natural Sciences Philadelphia Diatom Herbarium, USA.

Type locality. The new species was observed in a sample from Hat Creek (40.851099,−121.5364; 526PS1724) in Lassen National Forest in the Southern Cascade Mountain Range, California collected on 27 June 2016 by Jennifer York .

  • Author
    Stancheva 2018
  • Length Range
    15.7-40 µm
  • Width
    8.7-22 µm
  • Striae in 10µm

Cite This Page

Stancheva, R. (2020). Cocconeis cascadensis. In Diatoms of North America. Retrieved September 25, 2021, from https://diatoms.org/species/cocconeis-cascadensis


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