Landoltia & other duckweeds.

Family Araceae > Subfamily Lemnoideae.
Genera are Landoltia, Lemna, Spirodela, Wolffia and Wolffiella.

Duckweeds have the smallest flowers of all the angiosperms with some as small as 0.3 mm.
They are small plants that multiply rapidly and can form dense mats on, or just under the surface of, still water.

There are no stems or true leaves.
Plants only have 2 or 3 leaf-like structures a few cells thick with air sacs to keep them afloat.
They are often, apparently incorrectly, referred to as fronds or thalli.

Each ‘leaf’ can have from none to 21 fine roots depending on the species.
For example Lemna have 1 root, Landoltia punctata 2 to 5 and Spirodela 7 to 21.

Spirodela and Landoltia (the more primative species) have a tiny, thin, scalelike leaf (prophyllum)
    on both surfaces of the basal end.
It is usually best seen in young plants.

Duckweeds mostly reproduce asexually by budding.
A small pouch forms on the plant and new plants form in it.
These daughter plants may stay attached by a short stalk.

In Spirodela, Landoltia and Lemna the flat budding pouches are on both sides.
In Wolfiella there is a flat, triangular pouch at the base.
In Wolffia the basal pouch is funnel-shaped.

The rarely produced flowers are bisexual, under 1 mm, and consist of just 1 or 2 stamens and 1 carpel.
Flowers can be in a cavity or a budding pouch.