four-cut

Its flowers, which are purple, come on the otherwise naked stems of last season's growth, lateral fashion, in threes mostly, and sometimes the blossomed stems will be over a foot in length; the flowers are ½in. long, sessile and funnel-shaped; the limb four-cut; sweet smelling and very durable.

Hardy Perennials and Old Fashioned Flowers Describing the Most Desirable Plants, for Borders, Rockeries, and Shrubberies. John Wood