• Synonyms
    Schizonema pachycephalum (Cleve) Kuntze 1898

Identification

Description

Valves are lanceolate to sub-lanceolate. The apices are capitate and broadly rounded. The central area is a distinct fascia that widens slightly near the valve margins. The axial area is distinctly thickened and narrows toward the apices. The raphe is straight. Proximal raphe ends are slightly expanded. Terminal raphe fissures are sigmoid; they are hooked to opposite sides and widen at the ends. The striae are radiate in the center of the valve and become convergent near the apices.

Striae are difficult to resolve with light microscopy because the areolae are entirely covered by external hymenes.

This taxon is unusual within the genus Envekadea for the presence of a fascia and fine striae. It is also unusual for its broad environmental tolerance (see AUTECOLOGY section).

Autecology

Envekadea pachycephala was collected in Everglades National Park, Florida and the Arthur R. Marshall Loxahatchee National Wildlife Refuge (LNWR). It was found within benthic flocculent detritus, Utricularia purpurea (bladderwort), and recently burned Cladium jamaicense (sawgrass). The taxon is very rare in Florida (< 6% relative abundance), with the greatest abundances found in LNWR, a distinctive, soft-water environment of the Everglades. The waters of LNWR are low in conductivity (97-263 μS/cm), pH (5.2-7.6) and total phosphorus (405-595 μg/g dry weight) of periphyton (E. Gaiser, unpublished data). The lower conductivity in the LNWR results from a deep peat layer that impedes direct biogeochemical interactions between the limestone bedrock, groundwater, surface water, and biota.

In North America, E. pachycephala has been documented in coastal marshes of Louisiana (Smith 2012).

Envekadea pachycephala has also been found around the world in an unusual combination of locations: South Africa, Sweden, Sri Lanka, Australia, New Zealand, Cuba, and Papua New Guinea. In these sites, this taxon occurs across broad salinity and nutrient conditions. Additional work on the ecophysiology of this taxon is warranted to define its salinity and nutrient tolerances (Atazadeh et al. 2014).

Original Description

Linear, gibbous in the middle and at the ends, which are broadly rounded and capitate. Striae oblique, very fine, about 29 in 0,01 mm., reaching the median line. Stauros reaching the margin. Median line straight. Terminal nodules turned in opposite direction.

Length 0,055 mm. Breadth 0,009 mm. PI. Ill, fig. 43, 100%.

Fresh or slightly brackish water, Baakens River, Port Elizabeth, South Africa in sample sent by Mr. Joshua (Cl. et Moll. N:o 197). This species comes nearest to St. desiderata Cl. (in Cl. et Grun. Arctische Diat. PI. Ill, fig. 58), which also has the terminal nodules turned in opposite direction, but the outline of this species is different and its striae are almost parallel and much coarser. Both belong to section parallel with Grunows section Pseudopleurosigma of Navicula.

  • Basionym
    Stauroneis pachycephala
  • Author
    Cleve 1881
  • Length Range
    45-60 µm
  • Width
    8-10 µm
  • Striae in 10µm
    24.5-29.5

Original Images

Ptcleve  Original Image  Stauroneis Pachycephala
Ptcleve  Original Description  Stauroneis Pachycephala

Cite This Page

Lee, S, and Atazadeh, E. (2015). Envekadea pachycephala. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/envekadea_pachycephala

Responses

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