• Category
  • Length Range
    12.7-19.3 µm
  • Width Range
    2.7-3.5 µm
  • Striae in 10 µm



Valves are narrow, semi-elliptic, and dorsiventral. The apices are protracted and ventrally deflected. The dorsal margin is smoothly or flatly arched to nearly flat in the middle and gradually arched toward the apices. The ventral margin is straight to slightly convex, with a central inflation. The raphe is straight. The proximal raphe ends are straight, or weakly dorsally deflected. The axial area is narrow. A ventral fascia is present and extends to the valve margin. Dorsal striae are radiate throughout, more widely spaced in the middle. Ventral striae are difficult to resolve in LM.


This taxon was described from Adobe Creek, Riverside County, California (33.51272, -117.27038). At the time of collection (7/14/2020), temperature was 21.7 C, alkalinity (as CaCO3) was 440 mg/L, specific conductance was 3410 µS/cm, pH was 7.37, O2 was 6.7 mg/L, turbidity was 1.86 NTU, and salinity was 1.92 ppt.

This taxon has also been found in other coastal streams in southern California (R. Stancheva, personal observations).

Original Description

Halamphora subtilis Stepanek & Kociolek sp. nov. (Figs 45–59)

Description. Valves are narrowly semi-elliptical and dorsiventral. The dorsal margin is smoothly arched near the apices, becoming flat over the center and the ventral margin is tumid. Valve length 14–18 μm, valve breadth 2.5–3.5 μm. Apices are protracted, capitate and weakly deflected ventrally. The raphe is straight, with straight to weakly dorsally deflected proximal raphe ends. The axial area is narrow throughout. Only a ventral fascia is present and extends to the margin. The dorsal striae, 21–25 in 10μm, are uninterrupted, radiate throughout and more widely spaced near the valve center. The ventral striae, 46–48 in 10μm, are difficult to resolve in LM. In SEM, the raphe is straight both internally and externally (Figs 55, 58), with the external proximal ends nearly straight (Fig. 56) and the distal ends sharply hooked dorsally (Fig. 57). The dorsal raphe ledge is prominent, composed of a thin siliceous flap running uninterrupted the length of the valve (Fig. 55, arrow). The dorsal striae are separated by thick costal ribs and are coarsely and somewhat irregularly uni- to triseriate both externally (Fig. 57) and internally (Fig. 59). The dorsal costae at center are distinctly thickened both externally (Fig. 55, arrowhead) and internally (Fig. 58, arrow). No dorsal marginal ridge is present, although striae are crossed by thin, irregularly placed intercostal ribs near the dorsal margin (Fig. 56, arrows). The ventral striae are small and fine (Figs 55, 58).

Holotype. Slide and material ANSP GC 64903, Academy of Natural Sciences, Philadelphia, USA. Holotype specimen illustrated in Fig. 46. Isotype. Slide and material JPK 8362, University of Colorado, Museum of Natural History Diatom Herbarium, Boulder, USA.

Type locality. Adobe Creek (33.51272, -117.27038), rock scrape, Riverside County, California, USA. Collected by J.P. Kociolek, November 2008.

  • Author
    Stepanek and Kociolek 2013
  • Length Range
    14–18 µm
  • Width
    2.5–3.5 µm
  • Striae in 10µm
    Dorsal striae 21–25 in 10 μm; ventral striae 46-48 in 10 μm

Original Images

Halamphora subtilis orig illus

Cite This Page

Ciugulea, I., Stancheva, R. (2020). Halamphora subtilis. In Diatoms of North America. Retrieved September 25, 2021, from https://diatoms.org/species/halamphora-subtilis


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