Oenothera

Oenothera is a genus of about 145[3] species of herbaceous flowering plants native to the Americas.[4] It is the type genus of the family Onagraceae. Common names include evening primrose, suncups, and sundrops. They are not closely related to the true primroses (genus Primula).

"Sundrop" redirects here. For the soft drink, see Sun Drop. For the fruit tree, see Eugenia victoriana.
"Evening Primrose" redirects here. For the musical, see Evening Primrose (musical).
"Suncup" redirects here. For the snow surface texture, see Suncup (snow).

Oenothera
Oenothera biennis
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Myrtales
Family: Onagraceae
Subfamily: Onagroideae
Tribe: Onagreae
Genus: Oenothera
L.[1]
Species

145 species (188 taxa) in 18 sections, including:
O. affinis
O. acaulis
O. albicaulis
O. arequipensis
O. argillicola
O. bahia-blancae
O. biennis
O. brachycarpa
O. caespitosa
O. californica
O. canescens
O. catharinensis
O. cavernae
O. cinerea
O. clelandii
O. coloradensis
O. coquimbensis
O. coronopifolia
O. curtiflora
O. curtissii
O. deltoides
O deltoides ssp. howellii
O. drummondii
O. elata
O. elongata
O. featherstonei
O. flava
O. fraserii
O. fruticosa
O. gaura
O. glaucifolia
O. glazioviana
O. grandiflora
O. grandis
O. harringtonii
O. hartwegii
O. heterophylla
O. hexandra
O. howardii
O. humifusa
O. indecora
O. jamesii
O. laciniata
O. lamarckiana
O. lavandulifolia
O. lindheimeri
O. linifolia
O. longissima
O. longituba
O. macrocarpa
O. mendocinensis
O. mexicana
O. mollissima
O. montevidensis
O. nana
O. nutans
O. oakesiana
O. odorata
O. pallida
O. parodiana
O. parviflora
O. pedunculifolia
O. perennis
O. peruana
O. picensis
O. pilosella
O. primiveris
O. pubescens
O. punae
O. ravenii
O. rhombipetala
O. rosea
O. rubinervis
O. sandiana
O. santarii
O. scabra
O. serrulata
O. siambonensis
O. sinuosa
O. speciosa
O. stricta
O. stubbei
O. suffrutescens
O. tafiensis
O. tarijensis
O. tetraptera
O. triloba
O. tubicula
O. versicolor
O. villaricae
O. villosa
O. wolfii
O. xenogaura
O. xylocarpa

List sources :[2]

See: List of Oenothera species.

Description

The species vary in size from small alpine plants 10 centimeters tall, such as O. acaulis from Chile, to vigorous lowland species growing to 3 meters, such as O. stubbei from Mexico. The leaves form a basal rosette at ground level and spiral up to the flowering stems. The blades are dentate or deeply lobed (pinnatifid). The flowers 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 caespitosa, 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 the stigma, which has four branches in an X shape.[6]

Ecology

Oenothera flowers are pollinated by insects, such as moths and bees. Like many other members of the Onagraceae, however, the pollen grains are loosely held together by viscin threads, so only insects that are morphologically specialized to gather this pollen can effectively pollinate the flowers. Bees with typical scopa cannot hold it. Also, the flowers open at a time when most bee species are inactive, so the bees which visit Oenothera are generally vespertine temporal specialists: bees that forage in the evening. The seeds ripen from late summer to fall.

Oenothera are used as food plants by the larvae of some Lepidoptera species, including the large white-lined sphinx.[7] The flower moths Schinia felicitata and S. florida both feed exclusively on the genus, and the former is limited to O. deltoides.

In the wild, some species of evening primrose act as primary colonizers, quickly appearing in recently cleared areas. They germinate in disturbed soils, and can be found in habitat types such as dunes, roadsides, railway embankments, and waste areas. They are often casual and are eventually out competed by other species.

Based on observations of evening primroses (Oenothera 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 flowers that have the job of the ears.[8]

Origin

The genus Oenothera may have originated in Mexico and Central America,[9][10] and spread farther north in North America and into South America. With the advent of international travel, species are now found in most temperate regions of the world. In Europe alone there are about 70 introduced species of Oenothera.[4] During the Pleistocene era a succession of ice ages swept down across North America, with intervening warm periods. This occurred four times, and the genus experienced four separate waves of colonization, each hybridizing with the survivors of previous waves.[10][11] This formed the present-day subsection Euoenothera. The group is genetically and morphologically diverse and the species are largely interfertile, so the species boundaries have been disputed amongst taxonomists.[9][12]

Genetics
Further information: Mutationism
Painting of Hugo de Vries, making a painting of an evening primrose, which had apparently produced new forms by large mutations in his experiments, by Thérèse Schwartze, 1918

The pattern of repeated colonizations resulted in a unique genetic conformation in the Euoenothera whereby the chromosomes at meiosis can form circles rather than pairs. This is the result of several reciprocal translocations between chromosomes such that the pairing occurs only at the tips. This phenomenon apparently has non-Mendelian genetic consequences; with this mode of chromosome segregation and a system of balanced-lethal genes, genetic recombination is prevented and the plants display the hybrid vigor of heterosis.[13] This resulted in the evolution of many sympatric races in North America east of the Rocky Mountains. Analysis of the cytology of these races and of artificial hybrids between them increased understanding of the genetic and geographic evolution of the Euoenothera. This subject was a major area of genetic research during the first half of the 20th century.[14][15]

The appearance of sudden changes in Oenothera lamarckiana led the pioneering geneticist Hugo de Vries to propose the theory of mutationism (Mutationstheorie) in 1901. This asserted that speciation 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.[16][17]

Taxonomy

Evening primroses were originally assigned to the genus Onagra, which gave the family Onagraceae its name. Onagra (meaning "(food of) onager") was first used in botany in 1587, and in English in Philip Miller's 1754 Gardeners Dictionary: Abridged. The modern name Oenothera was published by Carolus Linnaeus in his Systema Naturae. Its etymology is uncertain, but is believed to be derived from the Greek words ονος θηρας (onos theras), meaning "donkey catcher", or οινος θηρας (oinos theras), meaning "wine seeker".[18]

Dietary uses and side effects

Primrose is commonly sold as a dietary supplement in capsules containing the seed oil, and is advertised to treat various medical disorders, such as eczema, diabetic neuropathy, rheumatoid arthritis, or numerous other conditions.[19] The main phytochemical in primrose seed oil is gamma-linolenic acid.[19]

There is no high-quality scientific evidence that primrose or primrose oil has any effect on human diseases or promotion of health,[19][20] and specifically no evidence that it is effective to treat eczema[20] or cancer.[21]

Consuming 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 given prescription drugs as anticoagulants, such as warfarin.[22]

Cultivation

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 caespitosa), Mexican evening primrose (Oenothera berlanderii), and Saltillo evening primrose (Oenothera stubbei).[23]

Annual evening primroses are also popular ornamental plants in gardens. Many are fairly drought-resistant.

The first plants to arrive in Europe reached Padua from Virginia in 1614 and were described by the English botanist John Goodyer in 1621. Some species are now also naturalized in parts of Europe and Asia, and can be grown as far north as 65°N in Finland. The UK National Council for the Conservation of Plants and Gardens, based at Wisley, maintains an Oenothera collection as part of its National Collections scheme.

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References
  1. "Genus: Oenothera L". Germplasm Resources Information Network. United States Department of Agriculture. 2004-03-22. Archived from the original on 2010-09-14. Retrieved 2010-10-28.
  2. "GRIN Species Records of Oenothera". Taxonomy for Plants. USDA, ARS, National Genetic Resources Program. Retrieved July 11, 2010.
  3. Singh, S.; et al. (2012). "An updated review on the Oenothera genus" (PDF). J. Chin. Integr. Med. 10 (7): 717–25. doi:10.3736/jcim20120701.
  4. Mihulka, S.; Pyšek, P. (2001). "Invasion history of Oenothera congeners in Europe: a comparative study of spreading rates in the last 200 years" (PDF). Journal of Biogeography. 28 (5): 597–609. doi:10.1046/j.1365-2699.2001.00574.x.
  5. Gumbo Lily (Oenothera caespitosa). Native Wildflowers of the North Dakota Grasslands. USGS Northern Prairie Wildlife Research Center.
  6. Peterson, R. T. and M. McKenny (1968). A Field Guide to Wildflowers of Northeastern and North-central North America. Boston: Houghton Mifflin. ISBN 978-0-395-91172-3.
  7. "White-lined Sphinx Hyles lineata (Fabricius, 1775) | Butterflies and Moths of North America". www.butterfliesandmoths.org. Retrieved 2017-11-14.
  8. Nield, David (January 19, 2019). "Plants May Not Have Ears, But They Can 'Hear' Way Better Than We Thought". Science Alert.
  9. Raven, P. H.; et al. (1979). "An outline of the systematics of Oenothera subsect. Euoenothera (Onagraceae)". Systematic Botany. 4 (3): 242–252. doi:10.2307/2418422. JSTOR 2418422.
  10. Dietrich, W.; et al. (1997). Systematics of Oenothera section Oenothera subsection Oenothera (Onagraceae). Laramie: The American Society of Plant Taxonomists. ISBN 978-0-912861-50-0.
  11. Cleland, R. E. (1972). Oenothera - Cytogenetics and evolution. Boston: Academic Press. ISBN 978-0-12-176450-0.
  12. Rostanski, K. (1985). "The classification of subsection Oenothera (section Oenothera, Oenothera L., Onagraceae)". Feddes Report. 96 (1–2): 3–14. doi:10.1002/fedr.4910960103.
  13. Rauwolf, U.; et al. (2008). "Molecular marker systems for Oenothera genetics". Genetics. 180 (3): 1289–1306. doi:10.1534/genetics.108.091249. PMC 2581935. PMID 18791241.
  14. Cleland, R. E. (1972). Oenothera - Cytogenetics and Evolution. Boston: Academic Press. ISBN 978-0-12-176450-0.
  15. Harte, C. (1994). Oenothera - Contributions of a Plant to Biology. Berlin: Springer-Verlag. ISBN 978-3-540-53114-2.
  16. Endersby, Jim (2007). A Guinea Pig's History of Biology. Harvard University Press. pp. 148–162, 202–205. ISBN 978-0-674-02713-8.
  17. Ramsey, Justin; Ramsey, Tara S. (August 2014). "Ecological studies of polyploidy in the 100 years following its discovery". Phil. Trans. R. Soc. Lond. B. 5 (369): 898–900. doi:10.1098/rstb.2013.0352. PMC 4071525. PMID 24958925.
  18. Gledhill, D. (2008). The Names of Plants (4 ed.). Cambridge University Press. p. 278. ISBN 978-0-521-86645-3.
  19. "Evening primrose oil". National Center for Complementary and Integrative Health, US National Institutes of Health. 1 September 2016. Retrieved 24 June 2020.
  20. Bamford JT, Ray S, Musekiwa A, van Gool C, Humphreys R, Ernst E et al. (2013). "Oral evening primrose oil and borage oil for eczema". Cochrane Database of Systematic Reviews. 4 (4): CD004416. doi:10.1002/14651858.CD004416.pub2. PMID 23633319. CD004416.CS1 maint: uses authors parameter (link)
  21. "Gamma Linolenic Acid". American Cancer Society. 13 May 2010. Retrieved 13 August 2013.
  22. "Evening primrose". Drugs.com. 14 October 2019. Retrieved 24 June 2020.
  23. Jones W. and C. Sacamano. Landscape Plants for Dry Regions. Fisher Books. 2000. ISBN 1-55561-190-7
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