Oenothera[note 1] is agenus of about 145[3] species ofherbaceous flowering plantsnative to the Americas.[4] It is thetype genus of thefamilyOnagraceae. Common names includeevening primrose,suncups, andsundrops. They are not closely related to the true primroses (genusPrimula).
The species vary in size from smallalpine plants 10 centimeters tall, such asO. acaulis fromChile, to vigorous lowland species growing to 3 meters, such asO. stubbei fromMexico. Theleaves form a basal rosette at ground level and spiral up to the flowering stems. The blades are dentate or deeply lobed (pinnatifid). Theflowers of many species open in the evening, hence the name "evening primrose". They may open in under a minute. Most species have yellow flowers, but some have white, purple, pink, or red. Most native desert species are white.Oenothera cespitosa, a species of western North America, produces white flowers that turn pink with age.[5]One of the most distinctive features of the flower is thestigma, which has four branches in an X shape.[6]
Oenothera flowers arepollinated by insects, such asmoths andbees. Like many other members of the Onagraceae, however, thepollen grains are loosely held together byviscin threads, so only insects that aremorphologically specialized to gather this pollen can effectively pollinate the flowers. Bees with typicalscopa cannot hold it. Also, the flowers open at a time when most bee species are inactive, so the bees which visitOenothera are generallyvespertine temporal specialists: bees that forage in the evening. Theseeds ripen from late summer to fall.
Oenothera are used as food plants by thelarvae of someLepidoptera species, including the large white-lined sphinx (Hyles lineata).[7] The flower mothsSchinia felicitata andS. florida both feed exclusively on the genus, and the former is limited toO. deltoides.
In the wild, some species of evening primrose act asprimary colonizers, quickly appearing in recently cleared areas. They germinate indisturbed soils, and can be found in habitat types such asdunes, roadsides, railway embankments, and waste areas. They are often casual and are eventually out competed by other species.
Based on observations of evening primroses (O. drummondii), a study discovered that within minutes of sensing the sound waves of nearby bee wings through flower petals, the concentration of the sugar in the plant's nectar was increased by an average of 20 percent. Experiments were also conducted on flowers with the petals removed. No change in nectar production was noted, indicating that it is indeed the petals that sense sound.[8]
The genusOenothera may have originated inMexico andCentral America,[9][10] and spread farther north inNorth America and intoSouth America. With the advent of international travel, species are now found in most temperate regions of the world. In Europe alone there are about 70introduced species ofOenothera.[4] During thePleistocene era a succession ofice ages swept down across North America, with intervening warm periods. This occurred four times, and the genus experienced four separate waves of colonization, eachhybridizing with the survivors of previous waves.[10][11] This formed the present-day subsectionEuoenothera. The group isgenetically and morphologically diverse and the species are largely interfertile, so the species boundaries have been disputed amongsttaxonomists.[9][12]
The pattern of repeated colonizations resulted in a unique genetic conformation in theEuoenothera whereby thechromosomes atmeiosis can form circles rather than pairs. This is the result of severalreciprocal translocations between chromosomes such that the pairing occurs only at the tips. This phenomenon apparently hasnon-Mendelian genetic consequences; with this mode of chromosome segregation and a system ofbalanced-lethal genes,genetic recombination is prevented and the plants display the hybrid vigor ofheterosis.[13] This resulted in theevolution of manysympatric races in North America east of theRocky Mountains. Analysis of thecytology of these races and of artificial hybrids between them increased understanding of the genetic and geographic evolution of theEuoenothera. This subject was a major area of genetic research during the first half of the 20th century.[14][15]
The appearance of sudden changes inOenothera lamarckiana led the pioneering geneticistHugo de Vries to propose what he called "mutation theory" in 1901 (Mutationstheorie in the German the original article was written in).[16] This asserted thatspeciation was driven by sudden large mutations able to produce new varieties in a single step. The understanding that the observed changes in hybrids of the plant were caused by chromosome duplications (polyploidy) rather than gene mutation did not come until much later.[17][18]
Evening primroses were originally assigned to the genusOnagra, which gave the family Onagraceae its name.Onagra '[food of]onager' was first used inbotany in 1587, and in English inPhilip Miller's 1754Gardeners Dictionary: Abridged. The modern nameOenothera was published byCarolus Linnaeus in hisSystema Naturae. Itsetymology is uncertain, but it is believed to be derived from theGreek words οίνος θήρα (oinos thera) 'wine seeker'.[19]
The first species called by thecommon nameevening primrose wasOenothera biennis from eastern North America with the first use recorded by theOxford English Dictionary dating to 1761 in theThe Calendar of Flora, Swedish and English byBenjamin Stillingfleet.[20] Though there are stories of uncertain veracity that attribute the coinage to the botanistJohn Goodyer in the 1600s.[21] Older common names includedtree primrose andnight primrose.[20] Species that open in the morning rather than the evening are often calledsundrops, though most often in the United States. This name was first used in print in 1785.[22]
CertainOenothera plants have edible parts. Theroots ofO. biennis are reportedly edible in young plants. So are the flowers which have a sweet, crunchy taste.[23]
Consuming evening primrose oil may cause headache or stomach upset, may increase the risk of complications during pregnancy, and may increase the risk of bleeding in people givenprescription drugs asanticoagulants, such aswarfarin.[33]
A number of perennial members of the genus are commonly cultivated and used in landscaping in the southwestern United States. Popular species include tufted evening primrose (Oenothera cespitosa), Mexican evening primrose (Oenothera berlanderii), and Saltillo evening primrose (Oenothera stubbei).[34]
Annual evening primroses are also popularornamental plants in gardens. Many are fairlydrought-resistant.
The first plants to arrive in Europe reachedPadua fromVirginia in 1614 and were described by the English botanistJohn Goodyer in 1621. Some species are now alsonaturalized in parts ofEurope andAsia, and can be grown as far north as 65°N inFinland. The UK National Council for the Conservation of Plants and Gardens, based atWisley, maintains anOenothera collection as part of its National Collections scheme.
^ab"Genus:Oenothera L".Germplasm Resources Information Network. United States Department of Agriculture. 2004-03-22.Archived from the original on 2023-01-09. Retrieved2023-01-09.
^abDietrich, W.; et al. (1997).Systematics ofOenothera sectionOenothera subsectionOenothera (Onagraceae). Laramie: The American Society of Plant Taxonomists.ISBN978-0-912861-50-0.
^Cleland, R. E. (1972).Oenothera - Cytogenetics and Evolution. Boston: Academic Press.ISBN978-0-12-176450-0.
^Harte, C. (1994).Oenothera - Contributions of a Plant to Biology. Berlin: Springer-Verlag.ISBN978-3-540-53114-2.
^de Vries, Hugo.Die Mutationstheorie. Versuche und Beobachtungen über die Entstehung von Arten im Pflanzenreich (in German), Leipzig, Veit & Comp., 1901-03.
^Endersby, Jim (2007).A Guinea Pig's History of Biology. Harvard University Press. pp. 148–162,202–205.ISBN978-0-674-02713-8.
^Oenothera biennis. Ohio Perennial and Biennial Weed Guide. The Ohio State University Extension.
^abcd"Evening primrose oil". National Center for Complementary and Integrative Health, US National Institutes of Health. 1 September 2016. Retrieved24 June 2020.
^McFarlin, B. L.; Gibson, M. H.; O'Rear, J.; Harman, P. (1999). "A national survey of herbal preparation use by nurse-midwives for labor stimulation".J Nurse-Midwifery.44 (3):205–216.doi:10.1016/S0091-2182(99)00037-3.PMID10380441.
^Adair, C. (September 2000). "Cervical Ripening And Labor Induction Nonpharmacologic Approaches to Cervical Priming and Labor Induction".Clinical Obstetrics & Gynecology.43 (3):447–454.doi:10.1097/00003081-200009000-00005.PMID10949749.
^Dove, Dorinda; Peter Johnson (May–June 1999). "Oral evening primrose oil: Its effect on length of pregnancy and selected intrapartum outcomes in low-risk nulliparous women".Journal of Nurse-Midwifery.44 (3):320–324.doi:10.1016/S0091-2182(99)00055-5.PMID10380450.
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