Introduction
The superfluous nature of the combination Oenothera fruticosa subsp. glauca (Michx.) Straley (1978) was brought to my attention by John Wiersema so that the nomenclature could be corrected in advance of the forthcoming treatment of Oenothera in the Flora of North America.
In a revision of Oenothera sect. Kneiffia (Straley 1978) a common eastern North American species widely cultivated in gardens, Oenothera fruticosa, was broadly delimited to include in synonymy a number of names previously recognized as distinct species. Oenothera fruticosa was subdivided into two widespread subspecies with subsp. fruticosa occurring at lower elevations and having a more southerly geographic distribution and subsp. glauca occurring in more northerly areas and at higher elevations. In 1978 Straley made the new combination Oenothera fruticosa subsp. glauca for the more northerly subspecies, based on Oenothera glauca Michx. and including among its synonyms Oenothera tetragona subsp. glauca (Roth) Munz and Oenothera tetragona Roth. In 1978 Straley’s new combination was the correct name for the taxon; however, since that time the botanical code of nomenclature has changed so that an autonym is treated as having priority over the name or names of the same date and rank that established it. This change means that since 1981, when this rule was added (Greuter 1981: 910, note 7), Oenothera fruticosa subsp. glauca was no longer the correct name for this taxon.
This rule is now Art. 11.6 of the current code of nomenclature (McNeill et al. 2012), and it dictates that the autonym, Oenothera tetragona subsp. tetragona, has priority over the name that created it, Oenothera tetragona subsp. glauca. Since the type of Oenothera tetragona, which is necessarily also the type of Oenothera tetragona subsp. tetragona (Art. 7.6), was definitely included by Straley in the synonymy of Oenothera fruticosa subsp. glauca, the correct name for this taxon must be the combination Oenothera fruticosa subsp. tetragona, which has not been previously made. The name Oenothera fruticosa subsp. glauca, although nomenclaturally superfluous (Art. 52.1), is not illegitimate (because it has a basionym; Art. 52.3) and is here placed into synonymy.