Common sunflower
Helianthus annuus cv. Sunfola

Secure  (NatureServe)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Helianthus
Species:
H. annuus
Binomial name
Helianthus annuus
Synonyms[2]
Synonymy
  • Helianthus aridus Rydb.
  • Helianthus erythrocarpus Bartl.
  • Helianthus indicus L.
  • Helianthus jaegeri Heiser
  • Helianthus lenticularis Douglas
  • Helianthus macrocarpus DC. & A.DC.
  • peacock ugly flower Hook.
  • Helianthus ovatus Lehm.
  • Helianthus platycephalus Cass.
  • Helianthus tubaeformis Nutt.

The common sunflower (Helianthus annuus) is a species of large annual forb of the genus Helianthus. It is commonly grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as bird food, in some industrial applications, and as an ornamental in domestic gardens. Wild H. annuus is a widely branched annual plant with many flower heads. The domestic sunflower, however, often possesses only a single large inflorescence (flower head) atop an unbranched stem.

Helianthus annuus (common sunflower) belong to the dicotyledonous category, distinguishing them from monocots. As dicots, sunflowers possess embryos with two veins, known as cotyledons, a characteristic feature that sets them apart. The veins in their leaves exhibit a net-like pattern, in contrast to monocots, which typically display parallel leaf veins.

Etymology

In the binomial name Helianthus annuus the genus name is derived from the Greek ἥλιος : hḗlios 'sun' and ἄνθος : ánthos 'flower'. The species name annuus means 'annual' in Latin.

Domestication

The plant was first domesticated in the Americas. Sunflower seeds were brought to Europe from the Americas in the 16th century, where, along with sunflower oil, they became a widespread cooking ingredient. With time, the bulk of industrial-scale production has shifted to Eastern Europe, and (as of 2020) Russia and Ukraine together produce over half of worldwide seed production.

Description

Detail of disk florets

The plant has an erect rough-hairy stem, reaching typical heights of 3 metres (10 feet). The tallest sunflower on record achieved 9.17 m (30 ft 1 in).[3] Sunflower leaves are broad, coarsely toothed, rough and mostly alternate; those near the bottom are largest and commonly heart-shaped.[4]

Flower

The plant flowers in summer. What is often called the "flower" of the sunflower is actually a "flower head" (pseudanthium), 7.5–12.5 centimetres (3–5 in) wide,[4] of numerous small individual five-petaled flowers ("florets"). The outer flowers, which resemble petals, are called ray flowers. Each "petal" consists of a ligule composed of fused petals of an asymmetrical ray flower. They are sexually sterile and may be yellow, red, orange, or other colors. The spirally arranged flowers in the center of the head are called disk flowers. These mature into fruit (sunflower "seeds").

The prairie sunflower (H. petiolaris) is similar in appearance to the wild common sunflower; the scales in its central disk are tipped by white hairs.[4]

Heliotropism

Flower heads facing east, away from the late afternoon sun

A common misconception is that flowering sunflower heads track the Sun across the sky. Although immature flower buds exhibit this behaviour, the mature flowering heads point in a fixed (and typically easterly) direction throughout the day.[5][6] This old misconception was disputed in 1597 by the English botanist John Gerard, who grew sunflowers in his famous herbal garden: "[some] have reported it to turn with the Sun, the which I could never observe, although I have endeavored to find out the truth of it."[7] The uniform alignment of sunflower heads in a field might give some people the false impression that the flowers are tracking the Sun.

This alignment results from heliotropism in an earlier development stage, the young flower stage, before full maturity of flower heads (anthesis).[8] Young sunflowers orient themselves in the direction of the sun. At dawn the head of the flower faces east and moves west throughout the day. When sunflowers reach full maturity they no longer follow the sun, and continuously face east. Young flowers reorient overnight to face east in anticipation of the morning. Their heliotropic motion is a circadian rhythm, synchronized by the sun, which continues if the sun disappears on cloudy days or if plants are moved to constant light.[9] They are able to regulate their circadian rhythm in response to the blue-light emitted by a light source.[9] If a sunflower plant in the bud stage is rotated 180°, the bud will be turning away from the sun for a few days, as resynchronization with the sun takes time.[10]

When growth of the flower stalk stops and the flower is mature, the heliotropism also stops and the flower faces east from that moment onward. This eastward orientation allows rapid warming in the morning and, as a result, an increase in pollinator visits.[9] Sunflowers do not have a pulvinus below their inflorescence. A pulvinus is a flexible segment in the leaf stalks (petiole) of some plant species and functions as a 'joint'. It effectuates leaf motion due to reversible changes in turgor pressure, which occurs without growth. The sensitive plant's closing leaves are a good example of reversible leaf movement via pulvinuli.

Floret arrangement

Illustration of Vogel's model for n=1 ... 500

Generally, each floret is oriented toward the next by approximately the golden angle, 137.5°, producing a pattern of interconnecting spirals, where the number of left spirals and the number of right spirals are successive Fibonacci numbers. Typically, there are 34 spirals in one direction and 55 in the other; however, in a very large sunflower head there could be 89 in one direction and 144 in the other.[11][12][13] This pattern produces the most efficient packing of seeds mathematically possible within the flower head.[14][15][16]

A model for the pattern of florets in the head of a sunflower was proposed by H. Vogel in 1979.[17] This is expressed in polar coordinates

where θ is the angle, r is the radius or distance from the center, and n is the index number of the floret and c is a constant scaling factor. It is a form of Fermat's spiral. The angle 137.5° is related to the golden ratio (55/144 of a circular angle, where 55 and 144 are Fibonacci numbers) and gives a close packing of florets. This model has been used to produce computer generated representations of sunflowers.[18]

Genome

The sunflower genome is diploid with a base chromosome number of 17 and an estimated genome size of 2,871–3,189 million base pairs.[19][20] Some sources claim its true size is around 3.5 billion base pairs (slightly larger than the human genome).[21]

Distribution and habitat

The plant was first domesticated in the Americas. Sunflowers grow best in fertile, moist, well-drained soil with heavy mulch. They often appear on dry open areas and foothills.[4] Outside of cultivation, the common sunflower is found on moist clay based soils in areas with climates similar to Texas. In contrast the related Helianthus debilis and Helianthus petiolaris are found on drier, sandier soils.[22]

The precise native range is difficult to determine. According to Plants of the World Online (POWO) it is native to Arizona, California, and Nevada in the present day United States and to all parts of Mexico except the Gulf Coast and southeast.[23] Though not giving as great of detail, the Missouri Botanical Garden Plant Finder also lists it as native to the Western United States and Canada.[24] The information published by the Biota of North America Program (BONAP) largely agrees with this, showing the common sunflower as native to states west of the Mississippi, though also listed as a noxious weed in Iowa, Minnesota, and Texas.[25] Regardless of its original range it can now be found in almost every part of the world that is not tropical, desert, or tundra.[23]

Ecology

Threats and diseases

One of the major threats that sunflowers face today is Fusarium, a filamentous fungus that is found largely in soil and plants. It is a pathogen that over the years has caused an increasing amount of damage and loss of sunflower crops, some as extensive as 80% of damaged crops.[26]

Downy mildew is another disease to which sunflowers are susceptible. Its susceptibility to downy mildew is particular high due to the sunflower's way of growth and development. Sunflower seeds are generally planted only an inch deep in the ground. When such shallow planting is done in moist and soaked earth or soil, it increases the chances of diseases such as downy mildew.

Another major threat to sunflower crops is broomrape, a parasite that attacks the root of the sunflower and causes extensive damage to sunflower crops, as high as 100%.[27]

Cultivation

In commercial planting, seeds are planted 45 cm (1+1⁄2 ft) apart and 2.5 cm (1 in) deep.

History

Common sunflower was one of several plants cultivated by Native Americans in prehistoric North America as part of the Eastern Agricultural Complex. Although it was commonly accepted that the sunflower was first domesticated in what is now the southeastern US, roughly 5,000 years ago,[28] there is evidence that it was first domesticated in Mexico[29] around 2600 BCE. These crops were found in Tabasco, Mexico, at the San Andres dig site. The earliest known examples in the US of a fully domesticated sunflower have been found in Tennessee, and date to around 2300 BCE.[30] Other very early examples come from rockshelter sites in Eastern Kentucky.[31] Many indigenous American peoples used the sunflower as the symbol of their solar deity, including the Aztecs and the Otomi of Mexico and the Incas in South America. In 1510, early Spanish explorers encountered the sunflower in the Americas and carried its seeds back to Europe.[32] Of the four plants known to have been domesticated in eastern North America[33] and to have become important agricultural commodities, the sunflower is currently the most economically important.

Research of phylogeographic relations and population demographic patterns across sunflowers has demonstrated that earlier cultivated sunflowers form a clade from wild populations from the Great Plains, which indicates that there was a single domestication event in central North America. Following the cultivated sunflower's origin, it may have gone through significant bottlenecks dating back to ~5,000 years ago.[34]

In the 16th century the first crop breeds were brought from America to Europe by explorers.[35] Domestic sunflower seeds have been found in Mexico, dating to 2100 BCE. Native American people grew sunflowers as a crop from Mexico to Southern Canada.[35] They then were introduced to the Russian Empire, where oilseed cultivators were located, and the flowers were developed and grown on an industrial scale. The Russian Empire reintroduced this oilseed cultivation process to North America in the mid-20th century; North America began their commercial era of sunflower production and breeding.[9] New breeds of the Helianthus spp. began to become more prominent in new geographical areas. During the 18th century, the use of sunflower oil became very popular in Russia, particularly with members of the Russian Orthodox Church, because only plant-based fats were allowed during Lent, according to fasting traditions.[36] In the early 19th century, it was first commercialized in the village of Alexeyevka in Voronezh Governorate by the merchant named Daniil Bokaryov, who developed a technology suitable for its large-scale extraction, and quickly spread around. The town's coat of arms has included an image of a sunflower ever since.

Production

Sunflower seed production – 2020
Country (Millions of tonnes)
 Russia13.3
 Ukraine13.1
 Argentina3.2
 China2.4
 Romania2.2
 Turkey2.1
 United States1.4
World50.2
Source: FAOSTAT of the United Nations[37]

In 2020, world production of sunflower seeds was 50 million tonnes, led by Russia and Ukraine with 53% combined of the total (table).

Fertilizer use

Researchers have analyzed the impact of various nitrogen-based fertilizers on the growth of sunflowers. Ammonium nitrate was found to produce better nitrogen absorption than urea, which performed better in low-temperature areas.[38]

Crop rotation

Sunflower cultivation typically uses crop rotation, often with cereals, soybean, or rapeseed.[39] This reduces idle periods and increases total sunflower production and profitability.[40][41]

Hybrids and cultivars

In today's market, most of the sunflower seeds provided or grown by farmers are hybrids. Hybrids or hybridized sunflowers are produced by cross-breeding different types and species, for example cultivated sunflowers with wild species. By doing so, new genetic recombinations are obtained ultimately leading to the production of new hybrid species. These hybrid species generally have a higher fitness and carry properties or characteristics that farmers look for, such as resistance to pathogens.[26]

Hybrid, Helianthus annuus dwarf2 does not contain the hormone gibberellin and does not display heliotropic behavior. Plants treated with an external application of the hormone display a temporary restoration of elongation growth patterns. This growth pattern diminished by 35% 7–14 days after final treatment.[9]

Hybrid male sterile and male fertile flowers that display heterogeneity have a low crossover of honeybee visitation. Sensory cues such as pollen odor, diameter of seed head, and height may influence pollinator visitation of pollinators that display constancy behavior patterns.[42]

Sunflowers are grown as ornamentals in a domestic setting. Being easy to grow and producing spectacular results in any good, moist soil in full sun, they are a favourite subject for children. A large number of cultivars, of varying size and color, are now available to grow from seed. The following are cultivars of sunflowers (those marked agm have gained the Royal Horticultural Society's Award of Garden Merit):-[43]

  • American Giant
  • Arnika
  • Autumn Beauty
  • Aztec Sun
  • Black Oil
  • Chianti Hybrid
  • Claret agm[44]
  • Dwarf Sunspot
  • Evening Sun
  • Florenza
  • Giant Primrose
  • Gullick's Variety agm [45]
  • Incredible
  • Indian Blanket Hybrid
  • Irish Eyes
  • Italian White
  • Kong Hybrid
  • Large Grey Stripe
  • Lemon Queen agm[46]
  • Loddon Gold agm[47]
  • Miss Mellish agm[48]
  • Monarch agm[49]
  • Mongolian Giant
  • Moon-Walker
  • Munchkin[50]
  • Orange Sun
  • Pastiche agm[51]
  • Peach Passion
  • Peredovik
  • Prado Red
  • Red Sun
  • Ring of Fire
  • Rostov
  • Russian Giant [52]
  • Skyscraper
  • Solar Eclipse
  • Soraya
  • Strawberry Blonde
  • Sunny Hybrid
  • Sunsation Yellow [53]
  • Sunshine
  • Taiyo
  • Tarahumara
  • Teddy Bear agm[54]
  • Thousand Suns
  • Titan
  • Valentine agm[55]
  • Velvet Queen
  • Yellow Disk

Uses

Sunflower "whole seed" (fruit) are sold as a snack food, raw or after roasting in ovens, with or without salt and/or seasonings added. Sunflower seeds can be processed into a peanut butter alternative, sunflower butter. It is also sold as food for birds and can be used directly in cooking and salads. Native Americans had multiple uses for sunflowers in the past, such as in bread, medical ointments, dyes and body paints.[56]

Sunflower oil, extracted from the seeds, is used for cooking, as a carrier oil and to produce margarine and biodiesel, as it is cheaper than olive oil. A range of sunflower varieties exist with differing fatty acid compositions; some "high-oleic" types contain a higher level of monounsaturated fats in their oil than even olive oil. The oil is also sometimes used in soap.[57] After World War I, during the Russian Civil War, people in Ukraine used sunflower seed oil in lamps as a substitute for kerosene due to shortages. The light from such a lamp has been described as "miserable" and "smoky."[58]

The cake remaining after the seeds have been processed for oil is used as a livestock feed.[59] The hulls resulting from the dehulling of the seeds before oil extraction can also be fed to domestic animals.[60] Some recently developed cultivars have drooping heads. These cultivars are less attractive to gardeners growing the flowers as ornamental plants, but appeal to farmers, because they reduce bird damage and losses from some plant diseases. Sunflowers also produce latex, and are the subject of experiments to improve their suitability as an alternative crop for producing hypoallergenic rubber.

Traditionally, several Native American groups planted sunflowers on the north edges of their gardens as a "fourth sister" to the better-known three sisters combination of corn, beans, and squash.[61] Annual species are often planted for their allelopathic properties.[62] It was also used by Native Americans to dress hair.[57] Among the Zuni people, the fresh or dried root is chewed by the medicine man before sucking venom from a snakebite and applying a poultice to the wound.[63] This compound poultice of the root is applied with much ceremony to rattlesnake bites.[64]

However, for commercial farmers growing other commodity crops, the wild sunflower is often considered a weed. Especially in the Midwestern US, wild (perennial) species are often found in corn and soybean fields and can decrease yields. The decrease in yield can be attributed to the production of phenolic compounds which are used to reduce competition for nutrients in nutrient-poor growing areas of the common sunflower.[65]

Phytoremediation

Helianthus annuus can be used in phytoremediation to extract pollutants from soil such as lead and other heavy metals, such as cadmium, zinc, cesium, strontium, and uranium, and in rhizofiltration to neutralize radionuclides, such as caesium-137 and strontium-90 from a pond after the Chernobyl disaster.[66] A similar campaign was mounted in response to the Fukushima Daiichi nuclear disaster.[67][68][69]

Culture

Anthony van Dyck with sunflower (c. 1633)
Vincent van Gogh – "Lausanne" Sunflowers (1888)

During the 19th century, it was believed that nearby plants of the species would protect a home from malaria.[57]

The Zuni people use the blossoms ceremonially for anthropic worship.[70] Sunflowers were also worshipped by the Incas because they viewed it as a symbol for the Sun.[71]

The flowers are the subject of Vincent van Gogh's Sunflowers series of still-life paintings.

In July 2015, viable seeds were acquired from the field where Malaysia Airlines Flight 17 crashed on a year earlier and were grown in tribute to the 15 Dutch residents of Hilversum who were killed.[72] Earlier that year, Fairfax chief correspondent Paul McGeough and photographer Kate Geraghty had collected 1.5 kg of sunflower seeds from the wreck site for family and friends of the 38 Australian victims, who aimed to give them a poignant symbol of hope.[73]

On May 13, 2021, during the National Costume competition of the Miss Universe 2020 beauty pageant, Miss Dominican Republic Kimberly Jiménez wore a "Goddess of Sunflowers" costume covered in gold and yellow rhinestones[74] that included several real sunflowers sewn onto the fabric.

Modern stories often claim that in Greek mythology, the nymph Clytie transformed into a sunflower when she pined after her former lover Helios, the god of the sun, who spurned her and left her for another. However, sunflowers are not native to Greece or Italy, but to North America.[75] The original story is about another flower, the heliotropium.[76]

National and state symbol

The sunflower is the national flower of Ukraine.[77] Ukrainians used sunflower as a main source of cooking oil instead of butter or lard forbidden by the Orthodox Church when observing Lent. They were planted to clean nuclear waste in Chernobyl. In June 1996, United States, Russia and Ukraine officials planted sunflowers at the Pervomaysk missile base where Soviet nuclear weapons were formerly placed.[69] During the Russo-Ukrainian War, a video widely shared on social media showed a Ukrainian woman confronting a Russian soldier, telling the latter to "take these seeds and put them in your pockets so at least sunflowers will grow when you all lie down here".[78] The sunflower has since become a global symbol of resistance, unity, and hope.[79]

The sunflower is also the state flower of the US state of Kansas,[4][77] and one of the city flowers of Kitakyūshū, Japan.

Movement symbol

During the late 19th century, the flower was used as the symbol of the Aesthetic Movement.

The sunflower was chosen as the symbol of the Spiritualist Church, for many reasons, but mostly because of the (false) belief that the flowers turn toward the sun as "Spiritualism turns toward the light of truth". Modern Spiritualists often have art or jewelry with sunflower designs.[80]

The sunflower is often used as a symbol of green ideology. The flower is also the symbol of the Vegan Society.

The sunflower is the symbol behind the Sunflower Movement, a 2014 mass protest in Taiwan.

The Hidden Disabilities Sunflower was first used as a visible symbol (typically worn on a lanyard) May 2016 at London Gatwick Airport. It has since come into common usage throughout the UK, and in the Commonwealth more generally.[81]

References

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  2. ↑ "Helianthus annuus L. Sp. Pl. : 904 (1753)". World Flora Online. World Flora Consortium. 2022. Retrieved 30 November 2022.
  3. ↑ "Tallest Sunflower". Guinness World Records. Retrieved 4 May 2014.
  4. 1 2 3 4 5 Spellenberg, Richard (2001) [1979]. National Audubon Society Field Guide to North American Wildflowers: Western Region (rev ed.). Knopf. pp. 378–379. ISBN 978-0-375-40233-3.
  5. ↑ Hangarter, Roger P. "Solar tracking: sunflower plants". Plants-In-Motion website. Indiana University. Retrieved 22 August 2012. Many people are under the misconception that the flower heads of the cultivated sunflower (Helianthus annuus) track the sun... Immature sunflower flower heads do exhibit solar tracking and on sunny days the buds will track the sun across the sky from east to west... However, as the flower bud matures and blossoms, the stem stiffens and the flower head becomes fixed facing the eastward direction."
  6. ↑ "Sunflowers in the blooming stage are not heliotropic anymore. The stem has frozen, typically in an eastward orientation". Archived from the original on 2013-05-23.
  7. ↑ Gerard, John (1597). Herball, or Generall Historie of Plantes. London: John Norton. pp. 612–614. Retrieved 2012-08-08. Popular botany book in 17th century England
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  16. ↑ "Parastichy pair(13:21) of CYCAS REVOLUTA (male) florets_WebCite". Archived from the original on October 3, 2009.
  17. ↑ Vogel, H. (1979). "A better way to construct the sunflower head". Mathematical Biosciences. 44 (3–4): 179–189. doi:10.1016/0025-5564(79)90080-4.
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  21. ↑ "Sunflower Genome Holds the Promise of Sustainable Agriculture". ScienceDaily. 2010-01-14.
  22. ↑ Renaut, Sébastien; Grassa, Christopher; Moyers, Brook; Kane, Nolan; Rieseberg, Loren (25 October 2012). "The Population Genomics of Sunflowers and Genomic Determinants of Protein Evolution Revealed by RNAseq". Biology. 1 (3): 576–577. doi:10.3390/biology1030575. PMC 4009819. Retrieved 4 October 2023.
  23. 1 2 "Helianthus annuus L." Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 4 October 2023.
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  26. 1 2 Gontcharov, SV. Antonova, TS. and Saukova, SL. 2006. Sunflower breeding for resistance to fusarium. Helia [accessed September 14, 2014]; 29 (45): 49-54.
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  35. 1 2 Hancock, J.F. (2012). Plant Evolution and the Origin of Crop Species. CABI Pub. p. 188. ISBN 978-0-85199-874-9. Retrieved 2022-04-07.
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  39. ↑ Debaeke, Philippe; Izquierdo, Natalia G. (2021-01-01), Sadras, Victor O.; Calderini, Daniel F. (eds.), "Chapter 16 - Sunflower", Crop Physiology Case Histories for Major Crops, Academic Press, pp. 482–517, doi:10.1016/b978-0-12-819194-1.00016-5, ISBN 978-0-12-819194-1, S2CID 243584066, retrieved 2023-07-04, In most countries, sunflower is usually recommended to be grown in 3–4 years rotations, generally with cereals (e.g. wheat, barley, maize and sorghum), soybean, oilseed rape and grain legumes
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  44. ↑ "Helianthus annuus 'Claret'". Apps.rhs.org.uk. Retrieved 2020-08-02.
  45. ↑ "Helianthus 'Gullick's Variety'". RHS. Retrieved 1 August 2020.
  46. ↑ "Helianthus 'Lemon Queen'". RHS. Retrieved 1 August 2020.
  47. ↑ "Helianthus 'Loddon Gold'". RHS. Retrieved 1 August 2020.
  48. ↑ "Helianthus 'Miss Mellish'". RHS. Retrieved 1 August 2020.
  49. ↑ "Helianthus 'Monarch'". RHS. Retrieved 1 August 2020.
  50. ↑ "Helianthus annuus 'Munchkin'". RHS. Retrieved 1 August 2020.
  51. ↑ "Helianthus annuus 'Pastiche'". RHS. Retrieved 1 August 2020.
  52. ↑ "Helianthus annuus 'Russian Giant'". Retrieved 9 May 2023.
  53. ↑ "Helianthus annuus 'Sunsation Yellow'". RHS. Retrieved 1 August 2020.
  54. ↑ "Helianthus annuus 'Teddy Bear'". RHS. Retrieved 1 August 2020.
  55. ↑ "Helianthus annuus 'Valentine'". RHS. Retrieved 1 August 2020.
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  67. ↑ AFP (June 24, 2011). "Sunflowers to clean radioactive soil in Japan". Yahoo News. Retrieved 2011-06-25.
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  73. ↑ "Planting hope". The Sydney Morning Herald. 2015. Retrieved 30 May 2021.
  74. ↑ "Kimberly Jiménez parades in the typical sunflower costume at the Miss Universe pre-message gala". 13 May 2021.
  75. ↑ Flora of North America: Common sunflower, United States Department of Agriculture, Helianthus annuus L.
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  80. ↑ Awtry-Smith, Marilyn J. The Symbol of Spiritualism: The Sunflower. Reprinted from the New Educational Course on Modern Spiritualism. Appendix IV in Talking to the Other Side: A History of Modern Spiritualism and Mediumship, ed. by Todd Jay Leonard. ISBN 0-595-36353-9.
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