Ivy Leaved Duckweed
Lemna trisulca
Usually most duckweeds are too invasive for a small pond but this species is not quite as vigorous and can be netted off if it gets out of hand.
Except during flowering time the light green leaves are just below the surface, each having a single rootlet and measuring 1cm across.
Spread indefinite
Hardy
Sun or shade
Propogation by division
