Williams and Reid 2006      Category: Eunotioid
TYPE SPECIES: Amphorotia clevei Williams and Reid




CLASS: Bacillariophyceae
  ORDER: Eunotiales
    FAMILY: Eunotiaceae

  1. Valves slightly, to stongly, asymmetric to the apical axis
  2. Valve symmetric to transapical axis
  3. Rimoportulae two per valve
  4. Valves greater than 60 µm in length

Valves of Amphorotia are large in size, generally greater than 60 µm in length. The valves are asymmetric to the apical axis and symmetric to the transapical axis. In addition, the frustules are asymmetric to the transapical plane, so that the dorsal mantle is very broad as compared to the ventral mantle. Each valve has two rimoportulae, positioned near the apices. The areaolae are coarse and not well organized into striae.

In North America, this taxon is only known as a fossil form. Extant populations of Amphorotia clevei are present in large oligotrophic Scandinavian and Baltic lakes. Endemic Amphorotia lineages are found in Lake Baikal, Mongolia’s Lake Hövsgöl, and in China.

Cite This Page:
Spaulding, S., and Edlund, M. (2009). Amphorotia. In Diatoms of the United States. Retrieved April 25, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - January 2009
Reviewer: Sam Rushforth - April 2010