Taxonomic changes in Oenothera sections Gaura and Calylophus (Onagraceae)

Abstract The long-recognized genus Gaura was shown recently to be deeply nested within one of two major clades of Oenothera. New molecular data indicate further taxonomic changes are necessary in Oenothera sect. Gaura. We make these changes here, including three new combinations, in advance of the Onagraceae treatment for the Flora of North America. The new phylogenetic studies show that several pairs of taxa treated as subspecies in the most recent revision by Raven and Gregory (1972) had independent origins within sect. Gaura, and are here elevated to species level (Oenothera nealleyi for Gaura suffulta subsp. nealleyi; Oenothera dodgeniana for Gaura neomexicana subsp. neomexicana; and Oenothera podocarpa for Gaura hexandra subsp. gracilis). Also, a nomenclatural problem in Oenothera sect. Calylophus is corrected by adopting the name Oenothera capillifolia Scheele for the species known previously, and nomenclaturally correct, as Calylophus berlandieri Spach. This problem necessitates a new combination Oenothera capillifolia subsp. berlandieri.

Phenology and distribution. Flowering from April to October. Trans-Pecos Texas and northern Coahuila, Mexico, north to Bernalillo and Torrance counties, New Mexico, in washes and other sandy places, grasslands, and extending to pinyon-juniper woodlands; 1220-2140 m. Raven and Gregory (1972) considered O. nealleyi to represent an unevenly intergrading entity with O. suff ulta based on geographical merging of some of the characteristics that distinguish them and because the entity from Terrell County, Texas, described as Gaura suff ulta var. terrellensis Munz has a combination of characteristics of the two taxa. Th e origin of these plants from Terrell County should be further explored. For now we here continue to include this name in the synonymy of O. nealleyi . Th e molecular data (Krakos 2011;unpubl.) suggest that O. nealleyi is not as closely related to O. suff ulta as suggested by Raven and Gregory (1972), given the placement in the phylogeny and the diff erence in scent profi les for these two taxa. Oenothera suff ulta is a member of a strongly supported clade (Fig. 1) consisting of it along with O. triangulata and O. patriciae, while O. nealleyi is a member of a polytomy that consists of other species of subsect. Gaura , with the O. suff ulta -O. triangulata -O. patriciae clade sister to it. Oenothera nealleyi has a strong sweet scent, characterized by benzaldehyde (almond), cinnamaldehyde, cinnamic alcohol (cinnamon), methyl salicylate and its methyl ether (wintergreen), neral and geranial (citronella), and nerol and geraniol (lemon) (R. Raguso, pers. comm.), whereas O. suff ulta does not have a discernible scent. Th is diff erence in scent probably plays a key role in the pollination syndromes for these species.  Raven & Gregory, 1972[1973  Gaura within a larger analysis of one of two major clades of Oenothera , which has been referred to as clade B by Wagner et al. (2007) with several outgroup species of the other major clade (A) of Oenothera from Krakos et al. (unpubl.). Th e phylogeny is based on nuclear sequences of ITS and ETS and the chloroplast markers rps16, ndhF, trnL-F, and rbcl . Th e labels use the most recent prior taxonomy, placing the group in Oenothera (Wagner et al. 2007), using the taxon delimitations of Raven and Gregory (1972). Th e taxa involved in the proposed changes here are in bold. Numbers above nodes indicate Bayesian posterior probability values.

Oenothera dodgeniana
Phenology and distribution. Flowering from June to September. In the western foothills of the San Juan Mountains in Archuleta County, Colorado, and Rio Arriba County, New Mexico; Sierra Blanca and Sacramento Mountains in Lincoln and Otero counties, south-central New Mexico. Collected once at Durango, La Plata County, Colorado (Raven and Gregory 1972), but has not since been recollected; found in mountain meadow openings in coniferous forests; 1830-2640 m.
Th e new name for this species is to honor David and Judy Dodgen of Cloudcroft, New Mexico, landowners who graciously allowed one of us (Krakos) to conduct research on their land, which harbors populations of this rare species. Oenothera dodgeniana and O. coloradensis were considered by Raven and Gregory (1972) to represent a relict species along the eastern fl ank of the Rocky Mountains that arose from more widespread species farther to the east, such as O. fi liformis . Th e new molecular analyses revealed that O. coloradensis is closely related to O. fi liformis (Fig. 1). Oenothera coloradensis is the fi rst branch of a subclade within the subsect. Biennial from a stout, fl eshy taproot, with several branches from the base, 50-80(-100) cm tall, strigillose proximally, becoming glandular puberulent and strigillose distally. Leaves: rosette leaves 4-18 × 1.5-4 cm; cauline leaves 5-13 × 1-4 cm, very narrowly elliptic, subglabrous or strigillose, margin subentire to repand-denticulate. Flowers 4-merous, opening at sunset; fl oral tube 8-12 mm; sepals 9.5-13 mm; petals 7-12 mm; staminal fi laments 6.5-9 mm, anthers 2.5-4 mm, pollen 90-100% fertile; style 19-25 mm. Capsule indehiscent, 6-8.5 × 2-3 mm, nut-like, hard, woody, not refl exed, the body ellipsoid or ovoid, sharply 4-angled, with fairly deep furrows alternating with the angles for 2-3 mm from the apex, ribbed from base of furrow to base of the fruit. Seeds 1-4, 2-3 mm, yellowish to light brown. Gametic chromosome number: n = 7. Probably self-compatible.
Phenology and distribution. Flowering in July and August. In early successional vegetation of the North and South Platte River watersheds on the high plains, sloping fl oodplains, and drainage base in heavy soils, from southern Laramie and Platte counties in Wyoming, northern Weld County, Colorado, formerly near Fort Collins, Larimer County, Colorado, and in western Kimbal County, Nebraska;1530-1950 Th e Colorado butterfl y plant is currently known from fewer than two dozen populations and has been federally listed as a Th reatened species in the U.S. (USDI Fish and Wildlife Service 2000). Th e primary threats are agricultural use of habitat, herbicide spraying to control weed species, and livestock trampling and grazing (see Fertig 2000, Heideland Handley 2011, NatureServe 2013. Recent study by Krakos (unpubl.) has determined this species to probably be self-compatible. Annual herb from a stout taproot, usually well-branched at the base and above, 15-100 cm tall, villous proximally, the leaves subglabrous to densely short-villous, becoming subglabrous, strigillose and/or glandular puberulent distally. Leaves: rosette leaves lyrate, 3-15 × 0.5-1 cm; cauline leaves 1-9 × 0.1-0.8 cm, linear to very narrowly elliptic or narrowly lanceolate, sinuate-dentate to subentire, subsessile. Flowers 4-merous, opening at sunset; fl oral tube 6-10 mm; sepals 6-12 mm; petals 5.5-9.5 mm; fi laments 4-6 mm, anthers 2-3 mm, pollen 90-100% fertile; style 11-18.5 mm. Capsule indehiscent, 6-8 × 2-3 mm, nut-like, hard, woody, not refl exed, broadly winged on the angles and deeply furrowed between the angles, the body ellipsoid or narrowly obovoid, narrowed at the base but not stipitate. Seeds 4, 2-3 mm, ovoid, usually fl attened on one or several sides by crowding in the fruit, yellowish to reddish brown. Gametic chromosome number: n = 7. Self-compatible.

Oenothera podocarpa (Wooton & Standley
Phenology and distribution. Flowering from (May) June to October. In Arizona from eastern Mohave County south through the mountains of central Arizona to eastern Pima County and the southwestern quarter of New Mexico, and in Mexico southward in the Sierra Madre Occidental to eastern Sonora and throughout the western halves of Chihuahua and Durango, often in disturbed sites in or on sandy washes, slopes, grasslands, meadows, pinyon-juniper or ponderosa pine woodlands, and sometimes on volcanic cinders; 760-2750 m.
Oenothera podocarpa is the fi rst species to branch off in the subsect. Gaura clade (Fig. 1), whereas O. hexandra is nested well within the subsect. Gaura clade. Th e epithet "podocarpa" was selected among the three equally available names at the species rank for this species. Previously, G. gracilis , one of four species published simultaneously by Wooton and Standley, was selected by Munz (1938), while placing the other three into synonymy. Tidestrom and Kittell (1941) apparently unaware of the Munz publication selected G. glandulosa , but were incorrect as they should have used G. gracilis . Th ey did not establish any new priority. Annual herb from a stout taproot, usually well-branched at the base and above, 15-100 cm tall, villous proximally, the leaves subglabrous to densely short-villous, and becoming subglabrous, strigillose, and/or glandular-puberulent distally. Leaves in a basal rosette and cauline; rosette leaves lyrate, gradually narrowed to the petiole, usually quickly deciduous; cauline leaves 1-9 × 0.1-0.8 cm, linear to very narrowly elliptic or narrowly lanceolate, margin sinuate-dentate to subentire, subsessile. Infl orescence strict to somewhat branched, 7-53 cm long, bracts 2-5 cm long, narrowly lanceolate to ovate. Flowers 3-merous, opening at sunset; fl oral tube 4.5-7.5 mm; sepals 3-10 mm; petals 4.5-7 mm; staminal fi laments 3-6 mm, anthers 1-2 mm, pollen 90-100% fertile; style 9-14.5 mm. Capsule indehiscent, 4.5-8 × 2-4.5 mm, nut-like, hard, woody, not refl exed, the body ellipsoid or narrowly obovoid, broadly winged on the angles and deeply furrowed between the angles, narrowed at the base but not stipitate. Seeds 3, 1.75-3 mm, ovoid, usually fl attened on one or several sides by crowding in the fruit, yellowish to reddish brown. Gametic chromosome number: n = 7. Self-compatible and highly autogamous.

Oenothera hexandra
Phenology and distribution. Flowering from March to November. From Durango, Mexico south in the Sierra Madre Occidental to the Trans Mexican Volcanic Belt, where abundant, and in Chiapas, Mexico as well as Guatemala in grasslands, meadows or oak woodlands, or disturbed areas, in sandy soils; 1800-2430 m.

Oenothera sect. Calylophus
A nomenclatural problem in Oenothera sect. Calylophus is corrected here by adopting the name Oenothera capillifolia Scheele for the species known previously, and nomenclaturally correct, as Calylophus berlandieri Spach when the genus Calylophus is recognized as distinct from Oenothera ; however, when this species is considered to be a member of Oenothera as it was recently by Wagner et al. (2007) based on molecular data (Levin et al. 2004), O. berlandieri (Spach) Steudel is not available since it is a later homonym. Th is problem necessitates a new combination Oenothera capillifolia subsp. berlandieri .  Towner (1977) subdivided Oenothera capillifolia into two subspecies. We here continue to use his classifi cation with the new nomenclature.