Plants free-floating on or below the surface of the water, not rooted in mud 2.

Land plants or aquatics rooted in mud 7.

Plants without obvious differentiation into stems and leaves 162. LEMNACEAE

Plants with obvious stems and leaves 3.

Leaves divided into numerous filiform segments 4.

Leaves not divided into numerous filiform segments 6.

Plants with small bladders on leaves or on apparently leafless stems 141. LENTIBULARIACEAE

Plants without small bladders 5.

Leaves dichotomously divided, the segments often again divided 31. CERATOPHYLLACEAE

Leaves pinnately divided, the segments simple 90. HALORAGACEAE

Perianth with a distinct calyx and corolla; petioles not inflated 151. HYDROCHARITACEAE

Perianth entirely petaloid; basal part of petioles inflated 171. PONTEDERIACEAE

Aquatic with rooted submerged stems (though often found detached and floating); submerged leaves in opposite pairs, petiolate; lamina initially palmately branched and then dichotomously or ternately divided into linear segments, forming a broad fan; floating leaves and flowers not found in the wild in Britain 30A. CABOMBACEAE

Not as above 8.

2- to 4-fid coloured staminodes present; leaves often fasciculate 52. CARYOPHYLLACEAE

Not as above 9.

Perianth absent, or of a single whorl, or of 2 or more whorls, all similar in shape, size, colour and texture 10.