• Category
  • Length Range
    23-46 µm
  • Width Range
    5.1-7.6 µm
  • Striae in 10 µm
    16-18 center (dorsal) up to 24 at the apices; 18-25 ventral side



Valves are rhombic-lanceolate and weakly dorsiventral. Apices are broadly rounded and not protracted, even in the smallest specimens. The axial area is narrow and continuous with the central area. Central area is slightly expanded on the dorsal side as a result of two or three shorter striae that are sometimes irregularly spaced. The raphe is lateral. Terminal raphe fissures are comma-shaped and deflected dorsally. Proximal raphe fissures are reverse-lateral and bent ventrally. Striae are radiate throughout. Striae are less dense near the central area, reaching up to 25 in 10 µm at the ventral apices. Areolae cannot be resolved under the light microscope.


Delicatophycus montana is common in the phytobenthos of mountain streams - cold, fast-flowing waters with low conductance and alkaline pH - in western Montana.

This taxon has also been verified from several streams in Pennsylvania. For example, Little Mahoning UPS Straight Run (40.824670, -78.9270), Rairigh Run (40.7857, -78.9374), Little Mahoning DWS (40.8204, -78.9820), Lacawaxan-Hawley (41.478522, -75183095), Laurel Hill Red Bridge (39.9525, -79.2706), Laurel Hill VFW (39.8206, -79.320830), Little Mahoning UPS Straight Run (40.824670, 78.9270). These materials are available at ANSP (GC 58421, GC 58423, GC 58427, GC 58437, GC 58449).

North Fork Teton River
Credit: Loren Bahls
North Fork of the Teton River on the Rocky Mountain Front in western Montana: home of Delicatophycus montana.

Original Description

Delicata montana sp. nov. Figures 85-90, 109-124

Valves are rhombic-lanceolate and slightly dorsiventral with a moderately arched dorsal margin and a somewhat less strongly arched (convex) ventral margin. Apices are rounded and not protracted. Valve length 23-46 µm; valve width 5.1-7.6 µm. The axial area is narrow; from the apices it follows the valve mid line to near the center, where it is displaced to the ventral side. The central area is small and asymmetric, typically formed by two shorter median striae on the dorsal side of the valve. The raphe is lateral and becomes weakly reverse-lateral near the proximal ends, which are also displaced ventrally. Terminal raphe fissures are comma-shaped and bent dorsally. Striae are radiate throughout and more widely spaced at the valve center (16-18 in 10 µm) than near the apices. Striae number 18-24 in 10 µm on the dorsal side, 18-25 in 10 µm on the ventral side, measured in a 10 µm segment adjacent to the central area. [n=104]

  • Author
    Bahls 2017
  • Length Range
    23-46 µm
  • Width
    5.1-7.6 µm
  • Striae in 10µm
    18-24 on the dorsal side, 18-25 on the ventral side

Original Images

Delicata Montana Original Images
Montana Delicata Species


Aug 21, 2023 - Transfer to Delicatophycus

From November 2018 to August 2023, this taxon appeared as Delicata montana Bahls 2017. Following Wynne (2019) the name Delicatophycus montana M.J.Wynne 2019 is a replacement name. - S. Spaulding

Cite This Page

Bahls, L. (2017). Delicatophycus montana. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/delicatophycus_montana


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