3-parted leaves occur on F. x intermedia, probably the most prevalent one in gardens - as represented by multiple cultivars including 'Lynwood' and 'Spring Glory'.
I should have gone on to say that the plant shown is liable to be the less prevalent F. suspensa, one of the parents of F. x intermedia - and the source of its sometimes 3-parted leaves. One of several ways it differs from the hybrid is its stems are hollow between the joints. There is an F. suspensa var. atrocaulis that produces dark stems like those pictured. There is a superior cultivar 'Nymans' present to some extent in gardens.
