• Category
  • Length Range
    32-59 µm
  • Width Range
    13.5–21.1 µm
  • Striae in 10 µm



Frustules are heterovalvar with a raphe valve and a rapheless valve. The valves are triundulate with the central valve margin wider than the apices, which are broadly rounded and capitate. Both valves are symmetric about the apical and transapical axes. The raphe valve face is concave about the transapical axis. On the raphe valve, the axial area is centered on the apical axis. The axial area is linear but narrows at the distal ends. A distinct transverse fascia is present in the central area. The raphe is slightly reverse lateral with expanded proximal ends. The proximal ends are unilaterally deflected. The distal raphe ends are deflected in the opposite direction. The distinctly uniseriate, punctate striae on the raphe valve are slightly radiate throughout and evenly spaced, 11 in 10 µm. The rapheless valve is convex about the transapical axis and does not have a fascia. On the rapheless valve, the narrow sternum is eccentric and positioned on the margin except where the valve center is expanded. The striae on the rapheless valve are distinctly punctate and have the same density as on the raphe valve. The rapheless valve striae are mostly parallel, tending to convergent and curved near the apices. Areolae on both valves are coarse and distinct, 11-12 in 10 µm. As a result of the concave and convex valve faces, the girdle view of A. inflata gives a recurved shape where the raphe valve valve fasica is on the inside of the curve.


Achnanthes inflata was common in epidendric samples from the woody plants Nyssa aquatica and Taxodium distichum (Fig. 2). The trees were sampled in an ephemeral wetland along the Cache River in northeast Arkansas. Other common species in the collection were Eunotia metamonodon, E. pectinalis, and Luticola mutica.

Water chemistry for the site: 22.5C, pH 7.28, conductivity 375 µS, NTU 8.63, dissolved oxygen 5.08 mg/L, NO3 0.345 mg/L, NO2 0.069 mg/L, orthophosphate 0.172 mg/L (Burge 2014).

Aichloro Copy
Credit: David Burge
Frustule in girdle view with two chloroplasts visible. Scale bar = 10 µm
Sample  Site Copy
Credit: David Burge
Sample site and substrates in the Cache River, Arkansas, where E. metamonodon was collected.
Credit: USGS BioData
Distribution of Achnanthes inflata in rivers of the continental U.S. based on the National Water Quality Assessment program. Retrieved 16 June 2015.

Original Description

  1. STAURONEIS INFLATA. Taf. 30. Fig. 22. (420/1). St. oblonga, media et apicibus late dilatata, bis constricta, late rotundato-truncata. Longet. 1/40 – 1/35’’’. Insel Trinidad; Krüger!
  • Basionym
    Stauroneis inflata
  • Author
    Kütz. 1844

Original Images

Achnanthes inflata orig illus
Achnanthes inflata orig descr

EMAP Assessment

EMAP Distribution

Achnanthes Inflata   Kùtzing   Grunow 40
Map 40

Response Plots

Achnanthes Inflata


Jun 22, 2018 - Update to size range.

Image added and text size range expanded to incorporate specimens sampled from Lake Catherine State Park, AR

Cite This Page

Burge, D. (2012). Achnanthes inflata. In Diatoms of North America. Retrieved June 22, 2018, from https://diatoms.org/species/achnanthes_inflata


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