• Category
  • Length Range
    74.2-113.2 µm
  • Width Range
    10.3-14.1 µm
  • Striae in 10 µm
    9-12

Identification

Description

Valves are lanceolate-clavate, with a rounded headpole and a narrower footpole. Striae are parallel to slightly radiate at the center of the valve, becoming more radiate near the apices. Striae are composed of a single row of distinct areolae that number 25-30 in 10 µm. The central axial area is wide and each branch is lanceolate. The central area is large, asymmetric and rectangular to elliptic. One side of the central area extends all the way to the valve margin; the other side is delimited by 3-5 shortened striae. One isolated stigma is located close to the proximal raphe ends on one side of the central nodule. The raphe is strongly lateral. Proximal raphe ends are small and inconspicuous. On deep focus, the internal proximal raphe ends are steeply deflected, into the shape of a barb, on the same side as the stigma. Terminal raphe ends are comma-shaped. The terminal raphe end at the footpole bisects a distinct apical pore field.

This is a large and distinctive but quite uncommon taxon, with extant populations apparently restricted to the Cascade Mountains of California and Oregon.

Autecology

The specimens pictured here were collected from three streams in the Cascade Mountains of western Oregon. One of these streams, Bessie Creek, is shown below. At the time of collection, these streams had a mean conductivity of 38 µS/cm-1, pH of 7.1, mean temperature of 4.9 degrees C and mean dissolved oxygen of 12.86 mg/L. Given these water quality characteristics, the conclusion of Patrick & Reimer (1975) that G. semiapertum prefers “water with fairly high conductivity” is questionable.

The original collection examined by Grunow was from Shasta County in northern California. Patrick & Reimer (1975) also report Gomphonema semiapertum from Oregon and unverified records from Michigan and Illinois. In addition, it was reported as a Pliocene fossil from a freshwater lake deposit in Kansas (Hanna 1932).

Gomphonema Semiapertum Map
Credit: Google Earth
Distribution of Gomphonema semiapertum based on samples in the Montana Diatom Collection.
Orbes1017 2300
Credit: U. S. Forest Service
Bessie Creek, Klamath County, Oregon: home of Gomphonema semiapertum.
Orbes1019 B2305
Credit: U. S. Forest Service
Bessie Creek, Klamath County, Oregon: home of Gomphonema semiapertum.
Orbes1024 1109
Credit: U. S. Forest Service
Bessie Creek, Klamath County, Oregon: home of Gomphonema semiapertum.

Original Description

Gomphonema semiapertum was originally published without a description.

  • Author
    Grunow in Van Heurck 1880

Original Images

Gomphonema Semiapertum Origimag
Gomphonemasemiapertumorigdesc001

Cite This Page

Bahls, L. (2017). Gomphonema semiapertum. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/gomphonema_semiapertum

Responses

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