Species Status for a Sonoran Desert Annual Member of Oenothera sect. Anogra (Onagraceae)

Abstract

The taxon most recently known as Oenothera avita W. Klein subsp. arizonica (Munz) Klein is here elevated to species level. It is easily distinguished from the perennial taxa of this complex, currently treated as three subspecies of O. californica, by its annual habit with a taproot, stems thickened near the base and tapering toward the apex, buds with conspicuous purple spots, each spot at the base of a long hair, longer attenuate capsules, and pinnatifid leaves. In preparation of treatments for the Flora ofArizona and Flora of North America I here raise to specific level an annual member of Oenothera sect. Anogra. It has been most recently known as Oenothera avita Klein subsp. arizonica (Munz) Klein (Klein in Munz, 1965). In this paper I will review the biosystematic information about the plant and discuss why it should be treated at the rank of species. Munz (1931) described Oenothera deltoides Torrey & Fremont var. arizonica Munz for the distinctive plants of Oenothera sect. Anogra with an annual habit from a taproot, stems thickened near the base and tapering toward the apex, buds with conspicuous purple spots, each spot at the base of a long hair, longer attenuate capsules, and pinnatifid leaves from the Sonoran Desert in central and southwestern Arizona. That these distinctive populations deserved formal recognition has never been questioned; rather the controversy has been at what taxonomic level they should be recognized and to what taxon they were most closely related. Because of its annual habit Munz (1931) included it in the annual desert species O. deltoides. William Klein transferred it, based on detailed biosystematic study of several species of Oenothera sect. Anogra from the western United States (1962, 1964, 1970, in Munz, 1965), to the perennial species O. californica (S. Watson) S. Watson in 1962. This species included four subspecies: subsp. calmfomica from southern California, subsp. avita Klein from interior California to northern Arizona, Nevada, and southwestern Utah, subsp. eurekensis (Munz & Roos) Klein, and subsp. arizonica. He later restricted the circumscription of 0. californica to include only the more western taxon (subsp. californica) of the complex because it was an autotetraploid, and the other taxa were diploid. He described a new species for the three diploid taxa, O. avita Klein. I have reviewed all of the information from past studies and compared the morphology in limited field studies and extensive herbarium study of all taxa included within O. deltoides, 0. californica, and its segregate O. avita. Recently, I treated the perennial autotetraploid populations (0. californica s. str.) and the diploid ones (0. avita) as one species (Wagner, 1993) because they share many morphological features, the differentiating characters intergrade extensively, and the polyploid taxon is an autotetraploid of apparent recent origin. Here I discuss the data on the Arizona annual populations and provide justification for proposing the new combination to recognize it as a distinct species. Klein transferred Oenothera deltoides var. arizonica to O. californica and then to O. avita primarily because it shared a high level of chromosomal end arrangements, differing from O. californica subsp. avita by only a single reciprocal translocation (5,, + O 4) in experimental crosses (1962, 1964, 1970). Additional data for his decision were obtained from pollen fertility of experimental hybrids. He easily obtained hybrids between the Arizona annual and both the perennial 0. avita subsp. avita and O. avita subsp. eurekensis. The hybrids had 62-96% and 54-99% pollen fertility, respectively, a similar level of fertility found in crosses between the perennial taxa of the complex, but more variable and usually somewhat lower fertility than interpopulational within-taxon crosses (Klein, 1964, 1970). He also obtained hybrids between O. avita subsp. arizonica and two of the subspecies of 0. deltoides, where this taxon had been originally placed by Munz. These hybrids had reduced pollen fertility ranging from 24% to 60% NOVON 8: 307-310. 1998. This content downloaded from 157.55.39.78 on Sun, 19 Jun 2016 07:03:23 UTC All use subject to http://about.jstor.org/terms