Oenothera L.
Family: Onagraceae
Oenothera image
Corey Raimond  

Key to Wisconsin Oenothera

    • 1a.Petals white, fading to pink or red, less than 15 mm long; fruits indehiscent, hard and nut-like, with 1--6 seeds; inflorescence often becoming a long, slender spike with numerous flowers 2

    • 1b.Petals yellow, or if pink or white, more than 15 mm long; fruit a dehiscent capsule, with many seeds; flowers solitary in leaf axils or many in a terminal raceme or spike 5

    • 2a.Strong perennials usually with a cluster of branches arising from a thick taproot; cauline leaves linear to narrowly-lanceolate, most 4--8 mm wide; fruit strigose-puberulent, pyramidal above, constricted below to a terete stipe-like base O. suffrutescens

    • 2b.Annuals or biennials, usually with a single unbranched stem; cauline leaves oblong to ovate-lanceolate, up to 5 cm wide; fruit glabrous or with spreading hairs, ellipsoid or fusiform, tapered at both ends 3

    • 3a.Flowers nearly actinomorphic; fruit usually glabrous; petals 1.5--3 mm long; stamen filaments without minute scales at base O. curtiflora

    • 3b.Flowers zygomorphic; fruit pubescent; petals 6--15 mm long; stamen filaments with minute scales at base 4

    • 4a.Plants up to 2 m tall, villous and glandular-puberulent, not strigillose, with many straight hairs O. gaura

    • 4b.Plants up to 4 m tall, strigillose with all hairs curled or appressed O. filiformis

    • 5a.Petals white, 15--40 mm long, fading to dingy pink or slighty yellow-white in pressed specimens; stems glabrous, the thin pale white epidermis exfoliating near base; flower buds nodding, solitary in leaf axils; seeds in one row in each locule O. nuttallii

    • 5b.Petals yellow or pale yellowish-white, fading to pale pink or turning red, orange, or purple, of varying lengths; stems pubescent, not exfoliating; flower buds erect; seeds in 2 rows in each locule 6

    • 6a.Floral tube (hypanthium) funnelform, prolonged less than 1 cm beyond ovary; stigma barely lobed; sepals with midrib keeled; leaves usually folded lengthwise, with sharply serrate margins O. serrulata

    • 6b.Floral tube slender, prolonged more than 1 cm beyond the ovary; stigma deeply 4-lobed; sepals not keeled; leaves mostly flat, not sharply serrate 7

    • 7a.Ovary 4-angled or narrowly 4-winged; fruit clavate to obovoid, sharply 4-angled or winged; plants perennial 8

    • 7b.Ovary and fruit more-or-less terete or obscurely 4-angled; plants annual or biennial 9

    • 8a.Petals 4--9 mm long; floral tube (hypanthium) 4--8 mm long; stems strigose-puberulent; leaves nearly entire O. perennis

    • 8b.Petals 13--30 mm long; floral tube 13--25 mm long; stems spreading-hirsute, the hairs 1--2 mm long; leaves denticulate O. pilosella

    • 9a.At least some (usually middle or lower) leaves coarsely pinnately lobed to pinnatifid or sinuate-laciniate; flowers solitary in leaf axils; plants annual O. laciniata

    • 9b.Cauline leaves linear, lanceolate, oblong, or ovate, with margins entire to serrate or denticulate, not coarsely pinnate; flowers several to many in a terminal spike or raceme; plants biennial, usually forming a basal rosette the first year 10

    • 10a.Capsule linear, slender, 2--3.2 mm thick, more than 5 times as long; seeds not sharply angled, finely pitted, ascending in the locules; flowers often numerous in long, dense spikes 11

    • 10b.Capsule lanceoloid, 4--8 mm thick at base, tapered upward, less than 5 times as long; seeds sharply angled, not pitted, horizontal in the locules; flowers often relatively few in short spikes 12

    • 11a.Petals 5--16 mm long; stigmas surrounded by anthers at about the same level O. clelandii

    • 11b.Petals 15--35 mm long; stigmas exserted above the anthers O. rhombipetala

    • 12a.Floral tube and petals each more than 3 cm long; styles 2--6 cm long, stigmas exserted above anthers O. glaziovianna

    • 12b.Floral tube and petals each less than 3 cm long; styles less than 2 cm long, stigmas surrounded by anthers at about the same level 13

    • 13a.Plants (or at least the inflorescences) appearing glabrous to the naked eye O. parviflora

    • 13b.Plants (including inflorescences) conspicuously pubescent 14

    • 14a.Subulate sepal tips in unopened buds contiguous at base, in reflexed sepals separated from the flat sepal by only a transverse line; inflorescence erect at anthesis; leaves lanceolate to ovate-lanceolate, or elliptical, 15--60 mm wide; capsules dull-green or gray-green 15

    • 14b.Subulate sepal tips slightly separated at base, slightly deflected outward in reflexed sepals, separated from the flat sepal by a small protuberance or shelf; inflorescence usually slightly arching or nodding at anthesis; leaves narrowly lanceolate, ovate, or oblong, 5--30 mm wide; shallowly repand-denticulate; capsules rusty brown or greenish-black 16

    • 15a.Plants densely strigillose; leaf blades thick, dull-green to gray-green; inflorescences gray, usually with dense, appressed non-pustulose pubescence, the internodes longer than the capsules O. villosa

    • 15b.Plants sparsely strigillose and villous, often also glandular puberulent; leaves thin, bright green; inflorescence green, dense with capsules longer than the internodes O. biennis

    • 16a.Plants densely minutely canescent-strigillose, often also with long appressed white non-pustulate hairs; leaves grayish-green narrowly oblanceolate to elliptic, 5--15 mm wide; capsules rusty brown O. oakesiana

    • 16b.Plants sparsely strigillose and villous with pustulate or non-pustulate hairs; leaves bright green, 10--30 mm wide; capsules greenish-black O. parviflora

About 150 species native to temperate and subtropical areas of North America and South America, with the center of diversity in the southwestern US and northern Mexico. Several species are naturalized nearly worldwide. More than 500 species have been described in the genus, most of these regarded as variants resulting from permanent translocation heterozygosity (PTH). Although the PTH breeding system is exclusively sexual, it produces hundreds of true-breeding lines similar to the apomictic microspecies of Hieracium, Rubus, Crepis, Taraxacum, etc. The identification of the broadly circumscribed species of recent treatments, especially in subsection Oenothera (couplets 12--16 in the key), often requires disregarding some atypical traits. The previously separate genera Gaura and Calylophus are inluded as sections of Oenothera in most recent treatments.