An Outline of the Systematics of Oenothera Subsect. Euoenothera (Onagraceae)

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Abstract
A new taxonomy is proposed for Oenothera subsection, Euoenothera (Onagraceae). In this group the species that are homozygous for the 3 major genomic complexes, A, B and C, are well separated from one another. Within each of these 3 complexes, species that form bivalents or relatively small rings of chromosomes are represented: AA (O. elata, O. longissima, O. jamesii), BB (O. grandiflora) and CC (O. argillicola). There are also complex heterozygotes with the AA (O. villosa, O. wolfii) and BB (O. austromontana) genomic constitutions. The entity that is called O. hookeri ssp. wolfii is an AA complex heterozygote, probably of separate origin from O. villosa and here accorded taxonomic recognition as a species, as is the BB homozygote previously called O. biennis ssp. austromontana. Each of the 3 possible combinations between the A, B and C genomes is recognized taxonomically: AB (O. biennis), AC (O. oakesiana, earlier considered a subspecies of O. parviflora) and BC (O. parviflora). O. glazioviana (O. lamarckiana auct., O. erythrosepala) has the constitution AB, like O. biennis, and may have originated following hybridization between O. biennis or O. grandiflora as the pistillate parent and O. elata (O. hookeri) as the staminate parent; this probably occurred in a garden in Europe. Minor forms, many of hybrid origin, that have originated in Europe are relegated to the species they resemble most closely. To recapitulate the taxonomic changes with respect to the most recent North American taxonomic treatment (Munz, 1965), the complex heterozygote O. wolfii (AA) is separated as a species from the bivalent-forming O. elata; O. austromontana (BB) is separated as a species from O. biennis (AB) and O. parviflora (BC; = Parviflora-1) is separated from O. oakesiana (AC; = Parviflora-2). The races that have been called Biennis-1, in which the B-complex is transmitted through the egg, and Biennis-2, in which the A-complex is transmitted through the egg, are not separated taxonomically, not usually being distinguishable in nature, despite the subspecific recognition accorded them by Munz. Among the non-complex-heterozygotes, O. hookeri is regarded as a synonym of O. elata because of the limited distinctiveness of these 2 entities as recognized earlier, and their broad geographical intergradation. O. glazioviana (1882) is an earlier name for what has recently been called O. erythrosepala (1903), and prior to that, O. lamarckiana by de Vries. Earlier attempts to create a taxonomy for this subsection, particularly in recent years in Europe, have split the species too finely for a general purpose taxonomy, mainly in imitation of genetic analyses but without the requisite genetic information in most cases to do this consistently.

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