Nitella flexilis, the smooth stonewort,[3] is a freshwater[4] species of characean algae that is used as a model organism for its large cell size and relative ease of cultivation in the laboratory.

A robust species growing up to a meter long with axes up to 1mm wide.

Branches in whorls once or twice divided.

[5] The species occurs on all continents of the world except Australia.

From the Eglinton Canal in Galway;[7] and in Counties Down and Londonderry;[8] River Dorree in Clare Island Co. Mayo 2004.