• Category
  • Length Range
    29-37 µm
  • Width Range
    8.0-9.5 µm
  • Striae in 10 µm
    14-15 on raphe valve, 12-13 on rapheless valve



Valves are linear-lanceolate, gibbous in the center valve, with broadly rounded ends.The raphe valve has a narrow axial area and a nearly rectangular central area extending to the valve margins. The proximal raphe ends are deflected slightly in one direction, with the distal ends curved strongly toward the mantle in the opposite direction. The axial on the rapheless valve is positioned near the valve margin. Striae are punctate and slightly radiate on raphe valve and parallel in the center. Striae on the rapheless valve are slightly radiate and curved near the apices.


Achnanthes tumescens was the most abundant and widely distributed species in collections from subaerial well walls of the Hawaiian islands of Oahu and Maui. It co-occurred with Pinnularia borealis, Hantzschia amphioxys and Diadesmis spp.

Original Description

Valves linear-lanceolate, swollen in the center, with broadly rounded ends, 22.0-36.5 µm long, 6.5-8.5 µm wide. Raphe valve with narrow axial area and a nearly rectangular central area extending to the valve margins (Figs 20-23). Raphe with proximal ends deflected slightly in one direction, with distal ends curved strongly towards mantle in opposite direction. Rapheless valve with axial area near valve margin (Figs 24-26). Striae punctate, slightly radiate on raphe valve (Figs 27, 28) on rapheless valve parallel in center, becoming slightly radiate with respect to the axial area, curved at the ends (Figs 29, 30), 15-17 in 10 µm on both valves. Puncta 16 in 10 µm on both valves.

  • Author
    R.L.Lowe and A.R.Sherwood 2009
  • Length Range
    22.0-36.5 µm
  • Width
    6.5-8.5 µm
  • Striae in 10µm

Original Images

Achnanthes tumescens orig illus
Achnanthes tumescens orig descr

Cite This Page

Lowe, R. (2011). Achnanthes tumescens. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/achnanthes_tumescens


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