Plant Aquatic with finely disected leaves, or plant terrestrial with moss-like leaves
Ovary Superior.
Leaves dichotomously forked............................fam Ceratophyllaceae
Leaves not dichotomously forked
Flowering or fruiting branches inflated.................fam Primulaceae
Flowering or fruiting branches not inflated
Corolla white; fruit indehiscent....................fam Cabombaceae
Corolla yellow, purple, or white; fruit dehiscent...........fam Lentibulariaceae
Ovary inferior..........................................................................fam Haloragaceae
Plant Not Aquatic, or leaves not finely dissected
Leaves toothed, lobed, dissected, or compound
Plant with 1 pair leaves and a solitary flower or fruit................fam Berberidaceae
Plant with more than 1 pair of leaves , or more than one fruit
Leaves deeply pinnately dissected
Petals yellow......................................fam Zygophyllaceae
Petals pink..............................................fam Geraniaceae
Leaves not deeply pinnately dissected
Corolla over 2 cm, leaves round, or flowers in racemes..fam Martyniaceae
Corolla less than 2 cm long, leaves not round, or flowers not in racemes
Ovary inferior
Leaves connate-perfoliate...................fam Dipsacaceae
Leaves not connate-perfoliate
Plant with a single whorl of 3 leaves.............fam Araliaceae
Plant with opposite leaves or leaves in more than one whorl
Stames 3.....................fam Valerianaceae
Stamens not 3
Inflorescence umbellate....................fam Apiaceae
Inflorescence not umbellate
Flowers and fruit in heads
Calyx present.......fam Apiaceae
Calyx absent.........fam Asteraceae
Flowers and fruit not in hea
or
Sepals 5............fam Saxifragaceae
Sepals 2 or 4....
Ovary Superior
Plant with latex or latex absent & flowers imperfect..fam Euphorbiaceae
Plant without latex, flowers perfect
Plant in fruit
Fruit 4 or 5 carpellate
Leaves thick and fleshy, not lobed....fam Crassulaceae
Leaves thin, not fleshy, lobed or dissected...fam Geraniaceae
Fruit 2 carpellate
Inforescence a cyme......fam Saxifragaceae
Inflorescence not a cyme...
Plant in flower
Corolla absent
Leaves dissected or lobed >1cm
Flowers imperfect......fam Cannabaceae
Flowers perfect.....fam Ranunculaceae
Leaves not, or very shallowly lobed
Inflorescence a terminal cyme...fam Saxifragaceae
Inflorescence a terminal pinacle or spike...
Corolla present...
(Radford, Ahles & Bell)