Cyprigedium calceolus (Yellow Lady Slipper) it is a member of the Orchid family.
What a beautiful plant this is. The flower is just coming on now and has a few days to go. This is another Wood-land plant from the Ontario Peninsula (for the description of the Ontario Peninsula it is two entries down in the Jack in the Pulpit).
These are delicate plants that do not like disturbance. This is a must know for a gardener. Be sure to plant it where it can stay for years to come.
Warning: Never pick the flowers as it can take up to seven years for it to re bloom if you do. This is not always the case, but, why take the chance. Also this plant is very toxic, so enjoy it, but show it due respect.