Azolla pinnata R.Br.

• a small free-floating plant (0.8-3 cm long) that is green, reddish-green or reddish-purple in colour.
• plants have a main stem with several branches regularly arranged on either side and are usually somewhat triangular in shape.
• these branches readily fragment from the base, leading to the formation of new plants.
• its roots have numerous fine side branches that give them a feathery appearance.
• its tiny overlapping 'leaves' (1-2 mm long) are alternately arranged along the branches and borne in two regular rows.

[From: Environmental Weeds of Australia]