The Buttercup family (Ranunculaceae) and Poppy family (Papaveraceae) are related and both are in the order "Ranunculales".
There are roughly 2,800 species in these two families around the world.

Bloodroot
 

Dutchman's
Breeches

Greater
Celandine

Lesser
Celandine

Marsh
Marigold

Meadow
Anemone

Meadow
Buttercup

Red
Baneberry

Red
Columbine

Tall
Thimbleweed

Winter
Aconite