lady slipper vs lady's-slipper

lady slipper and lady's-slipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
lady slipper	Yes	No	No	No
lady's-slipper	Yes	No	No	No

As nouns, lady slipper and lady's-slipper are synonyms defined as:

lady slipper and lady's-slipper: any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden

Other synonyms of lady slipper include ladies' slipper, lady's slipper, lady-slipper, slipper orchid.

lady slipper (noun)	lady's-slipper (noun)
any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden	any of several chiefly American wildflowers having an inflated pouchlike lip; difficult or impossible to cultivate in the garden