2. Gillenia trifoliata (Linnaeus) Moench, Suppl. Meth. 286. 1802.
Spiraea trifoliata Linnaeus, Sp. Pl. 1: 490. 1753; Porteranthus trifoliatus (Linnaeus) Britton
Leaves: stipules deciduous, linear, 3–8 × 1–3 mm (often with basal lobes), margins serrate to doubly serrate or shallowly laciniate; leaflet blade lanceolate, abaxial surface eglandular or sparsely sessile- or stipitate-glandular, otherwise glabrous or hairy, adaxial glabrous or sparsely to moderately hirsute. Hypanthia 5.5–8 mm. Petals 12–22 mm. Follicles short-beaked, smooth or slightly rugulose, loosely strigose to villous-strigose. 2n = 18.
Flowering Apr–Jul. Rich woods, open woods, commonly on rocky slopes, road banks and cuts; 100–1200 m; Ont.; Ala., Ark., Del., D.C., Ga., Ill., Ind., Ky., Md., Mass., Mich., Mo., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Va., W.Va.
Occurrences in Massachusetts and Rhode Island are escapes from cultivation. M. Oldham (pers. comm.) noted that Gillenia trifoliata has not been seen in Ontario for several decades and may be extirpated there.