All three have large white flowers (one inch across or more) with yellow stamens; the flowers are borne singly on long stems. Twinleaf flowers usually have eight petals and stamens, bloodroot has eight to sixteen petals and numerous stamens, and mayapple has six to nine petals and numerous stamens.
Bloodroot leaves, when older and fully opened, are sometimes confused with mayapple leaves.
Younger bloodroot leaves are sometimes not as elaborately lobed; possibly they could be mistaken for twinleaf, but it’s not likely.
Mayapple reproduction is mostly vegetative: the rhizomes form colonies, often vast, from which individual stems with single leaves emerge. But these plants don’t bloom. If you find some blooming, look at the plants and you’ll see that the stem forks and bears two leaves, with the flower growing at the junction. Only the two-leaved specimens will have flowers, though not all of them will.
Maypple can be found in rich, moist woodlands from the easternmost parts of the Great Plains to the Atlantic, and the Gulf of Mexico into Ontario and Quebec. It’s endangered in Florida.