Achnanthales

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thumb|Achnanthes lanceolata Achnanthes is a genus of diatoms belonging to the family Achnanthaceae.

Achnanthales is an order of diatoms.

Achnanthaceae is a family of algae belonging to the order Achnanthales, and was first described in 1844 by Friedrich Traugott Kützing.

Achnanthidiaceae is a family of diatoms in the order Achnanthales. It contains 461 species within 22 genera.

Achnanthidium is a genus of diatoms belonging to the family Achnanthidiaceae.