This species of dry western regions may just be adventive in eastern states (F). The only Ky. report is based on a coll. from a roadside in FULT (SIU): O'Dell & Windler #542, 30 Jun 1962; see also Mohlenbrock et al. (1966). However, L. McKinnney (NP) and V.Voelker (pers. comm. at NP) have doubted this identification, and they indicated that the coll. is probably a depauperate Oenothera laciniata (with long pilose hairs instead of the short stigose hairs expected in serrulata).. Calylophus (as a genus or section) differs from typical Oenothera as follows (W): stigmas peltate, disc-shaped or shallowly 4-lobed (versus deeply divided into 3-4 linear lobes); leaves linear to narrowly lanceolate or oblanceolate (versus narrowly to broadly lanceolate to oblanceolate), stiff, spinulose-serrate to subentire (versus subentire to deeply sinuate-lobed), less than 1 cm wide (up to 6+ cm wide); plants usually perennials less than 6 dm tall, often suffrutescent, stems several to many, branching from near base (versus annuals, biennials, or short-lived perennials, stems to 30 dm tall).