• Category
  • Length Range
    22.5-60 µm
  • Width Range
    5.6-7.7 µm
  • Striae in 10 µm
    13-15 at mid-valve, up to 17 at headpole



Valves are clavate with rounded apices. The raphe is lateral, becoming filiform at the proximal ends, where it slightly deflects unilaterally toward an isolated stigmoid. In some specimens, multiple isolated "ghost" puncta are found near the stigmoid. The axial area is large and rhombic, but it expands at mid-valve becoming more circular in shape.

Striae are weakly radiate throughout, becoming parallel to convergent at the headpole, and increasingly radiate at the footpole. Stria density increases slightly at the headpole. Areolae are not visibly distinct under LM.

At the footpole, the apical pore field is bifurcated.

In girdle view, frustules are rectangular to trapezoidal in shape. On the girdle bands, 1-2 rows of pores are present near the poles - and less so at mid-valve.

Under SEM, striae are found to be biseriate, composed of two rows of circular to slightly elliptic areolae. Multiple isolated puncta are found near the stigmoid at the central area.

This taxon has been confused with the European species, Gomphoneis rhombica (Fricke) Merino, García, Hernández-Mariné and Fernández 1994 (= Gomphonema rhombicum (Fricke) M.Schmidt 1904). Gomphoneis rhombica has dimensions of length as 36-53 µm, width 4.5-7.5 µm and striae of 9.5-12 in 10 µm (Iserentant and Ector 1996). Reports of G. rhombicum from Spain indicate a striae count up to 14 in 10 µm (Reichardt 2007).


Gomphonema amerhombicum appears to be common across the western United States. The type population is from Oak Creek, Arizona. Several more populations have been examined (see below). This taxon is relatively common in rivers, as sampled by the US Geological Survey National Water Quality Assessment (NAWQA) program from California, Washington and Oregon. The species was original described from New Mexico (Reichardt 2007).

G Amerhombicum Western Usa Populations   Ca Cl
Credit: Ian Bishop
Two distinct Gomphonema amerhombicum populations from two samples collected in the Sierra Nevada Mountains in California. Scale bars = 10 um.
G Amerhombicum Western Usa Populations   Or Cl
Credit: Ian Bishop
Two distinct Gomphonema amerhombicum populations from two samples collected in the Willamette Valley in Oregon. Scale bars = 10 um.
G Amerhombicum Western Usa Populations   Wa Cl
Credit: Ian Bishop
Two distinct Gomphonema amerhombicum populations from two samples collected in the Puget Sound Basin in Washington. Scale bars = 10 um.

Original Description

Frustula aspectu cingulari leviter cuneata serie punctorum distinctorum in prolongatione striarum in partibus distalibus limborum interrupta in media parte.

Valve minime gomphonemoideae-clavatae, lanceolatae verticibus obtuse vel paene late rotundatis plis basalibus angustius rotundatis. Longitudo 22.0-58.7 um, latitudo 5.5-7.6 um (cellulae primae usque ad 8.2 um). Raphe conspicue lateralis fissuris externis paene rectis fissuris internis distincte arcuatis non undulantibus. Extrema interna centralia declinata unilateraliter conspicue curtiora quam extrema externa apparentia. Area axialis modice lata lanceolata in media parte valvarum aream centralem late rhombicam formans. Stigma solitarium unilateraliter in nodulo centrali positum. Striae transapicales radiantes, 14-16 in 10 um sub vertices densiores,, 16-18 in 10 um. Striae seriebus duabus areolarum compositae, puncta in striis non aspectabilia in microscopio photonico.

  • Author
    E.Reichardt 2007
  • Length Range
    22.0-58.7 µm
  • Width
    5.5-7.6 µm
  • Striae in 10µm
    14-16 in the center valve, 16-28 at the ends

Original Images

Gomph Amerhobicum  Orig Descr
Gomph Amerhobicum  Orig Ill 1
Gomph Amerhobicum  Orig Ill 2

Cite This Page

Bishop, I., Potapova, M. (2017). Gomphonema amerhombicum. In Diatoms of North America. Retrieved September 25, 2021, from https://diatoms.org/species/gomphonema_amerhombicum


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