Oenothera Linnaeus sect. Epilobiopsis Spegazzini, Anales Soc. Ci. Argent. 48: 46. 1899; Boisduvalia Spach sect. Currania Munz; Epilobium sect. Currania (Munz) Hoch & P. H. Raven

Herbs annual, with taproot. Stems often with decumbent proximal branches, rarely simple, epidermis peeling proximally. Leaves opposite and early deciduous in proximal pairs, alternate distally, often crowded and exceeding internodes, caducous apical mucro often prominent. Flowers actinomorphic, usually cleistogamous; floral tube not bulbous, without scales inside; petals pink or white; pollen in tetrads; stigma clavate, subentire to ± shallowly 4-lobed. Cap­sules fusiform to subclavate, sharply 4-angled or terete, walls tough, usually splitting only in distal 1/3, central column disintegrating, sessile. Seeds 7–14 per locule in 2 rows, irregularly angular-fusiform; coma absent.

Species 2 (2 in the flora): w North America, nw Mexico, s South America.

Section Epilobiopsis, treated formerly as Boisduvalia sect. Currania (P. A. Munz 1941, 1965; P. H. Raven 1976), consists of two self-compatible, sometimes cleistogamous, annual species with n = 15 that occur primarily in western North America; Epilobium campestre also occurs disjunctly in southern Argentina. The species in this section are distinctive by lacking a seed coma and by being spring-blooming annuals (both features shared with sect. Pachydium), and uniquely by having tough, only partially dehiscent, capsules with seeds in two rows per locule (Raven and D. M. Moore 1965). Although the species of sect. Epilobiopsis share the gametic chromosome number n = 15 with those of sects. Cordylophorum and Zauschneria, all attempts have failed to form inter-sectional hybrids with those groups, as well as with species of sect. Pachydium (n = 9, 10, 19) with which they were formerly grouped (Munz 1965; S. R. Seavey 1992). Unexpectedly, molecular analyses (D. A. Baum et al. 1994; R. A. Levin et al. 2004) placed sect. Epilobiopsis as sister to a clade of sects. Pachydium and Zauschneria with strong support. Baum et al. also found weak support (81%) for the monophyly of sect. Epilobiopsis.