• Category
  • Length Range
    15-33 µm
  • Width Range
    5.1-6.2 µm
  • Striae in 10 µm
    16-18

Identification

Description

Valves clavate, with broadly rounded headpole. Four isolated stigmoids are present in line with most proximal full length striae. One or two shortened striae are present at each margin at the valve center. Striae are weakly radiate throughout, more radiate at the footpole and nearly parallel at the headpole. The raphe is straight.

This taxon is a member of the quadra-stigmoid gomphonemoids, a difficult and presently confusing group of closely related species. As with many diatom species complexes, the group is deserving of more work because 1) the type specimens or material of many taxa in the group are not available; 2) Taxa that were described by early authors were not adequately circumscribed. For example, the original description of Gomphonema olivaceoides var. densestriata appears to be based on a single valve, with a stria count of 18 in 10 µm; 3) This variety is distinguished based on stria count, and it is likely that the population has a far wider range in stria density; 4) In North America, particularly in the Northwest, there are a number of undescribed taxa in this group. The work of Bahls (personal communication, 2017) has uncovered a great deal of variability in this group.

Gomphonema olivaceoides var. densestriata should be compared closely with Gomphoneis pseudo-okunoi, which has a narrow range in stria density (13-15 in 10 µm).

Levkov and Williams (2011) described a diatom with a similar sounding name, Gomphonema densistriatum, from Lake Ohrid, Macedonia. That taxon, however, is heterotypic and bears little resemblance to G. olivaceoides var. densestriata.

Autecology

Gomphonema olivaceoides var. densestriata has been observed across the northern United States. Stoermer et al. (1999) note its presence in the Checklist of Diatoms from the Laurentian Great Lakes. Patrick and Reimer (1975) documented specimens from Lake Quinault on the Olympic Peninsula, Washington. Bahls (personal communication, 2017) recorded a large number of taxa closely related to this taxon from the Pacific Northwest.

Original Description

Differt a typo striis densioribus, 18 in 19 μ.

Deviates from the species by having the number of striae about 18 in 10 μ as against the number of the species which is only 11-12.

  • Author
    Foged 1963
  • Length Range
    19.3 µm
  • Width
    6.7 µm
  • Striae in 10µm
    18

Original Images

Gomphonema olivaceoides var. densestriata orig illus
G Olivaceoides Var Densistriata Orig Desc Text

Cite This Page

Bishop, I. (2017). Gomphonema olivaceoides var. densestriata. In Diatoms of North America. Retrieved November 16, 2019, from https://diatoms.org/species/gomphonema_olivaceoides_var._denstistriata

Responses

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