Nectar#Extrafloral nectaries

Nectar is derived from Greek νέκταρ, the fabled drink of eternal life.{{cite web|url=https://www.etymonline.com/word/nectar|title=Nectar|publisher=Online Etymology Dictionary, Douglas Harper|date=2018|access-date=28 May 2018}} Some derive the word from νε- or νη- "not" plus κτα- or κτεν- "kill"{{citation needed|date=October 2024}}, meaning "unkillable", thus "immortal". The common use of the word "nectar" to refer to the "sweet liquid in flowers", is first recorded in AD 1600.

A nectary or honey gland is floral tissue found in different locations in the flower and is one of several secretory floral structures, including elaiophores and osmophores, producing nectar, oil and scent respectively. The function of these structures is to attract potential pollinators, which may include insects, including bees and moths, and vertebrates such as hummingbirds and bats. Nectaries can occur on any floral part, but they may also represent a modified part or a novel structure.{{sfn|Rudall|2007|pages=96–98}} The different types of floral nectaries include:{{sfn|Nicolson et al|2017|page=41}}

• receptacle (receptacular: extrastaminal, intrastaminal, interstaminal)
• hypanthium (hypanthial)
• tepals (perigonal, tepal)
• sepals (sepal)
• petal (petal, corolla)
• stamen (staminal, androecial: filament, anther, staminodal)
• pistil (gynoecial: stigmatic, stylar)
• pistillodes (pistillodal, carpellodial)
• ovaries (ovarian: non-septal, septal, gynopleural)

Most members of Lamiaceae have a nectariferous disc which surrounds the ovary base and derived from developing ovarian tissue. In most Brassicaceae, the nectary is at the base of the stamen filament. Many monocotyledons have septal nectaries, which are at the unfused margins of the carpels. These exude nectar from small pores on the surface of the gynoecium. Nectaries may also vary in color, number, and symmetry.Willmer, Pat. Pollination and floral ecology. Princeton University Press, 2011.{{pn|date=December 2023}}{{isbn missing}} Nectaries can also be categorized as structural or non-structural. Structural nectaries refer to specific areas of tissue that exude nectar, such as the types of floral nectaries previously listed. Non-structural nectaries secrete nectar infrequently from non-differentiated tissues.{{sfn|Nicolson et al|2017}} The different types of floral nectaries coevolved depending on the pollinator that feeds on the plant's nectar. Nectar is secreted from epidermal cells of the nectaries, which have a dense cytoplasm, by means of trichomes or modified stomata. Adjacent vascular tissue conducts phloem bringing sugars to the secretory region, where it is secreted from the cells through vesicles packaged by the endoplasmic reticulum.{{cite journal |last1=Fahn |first1=Abraham |title=On the Structure of Floral Nectaries |journal=Botanical Gazette |date=1952 |volume=113 |issue=4 |pages=464–470 |doi=10.1086/335735 |jstor=2472434 |s2cid=85332036 }} The adjacent subepidermal cells may also be secretory.{{sfn|Rudall|2007|pages=96–98}} Flowers that have longer nectaries sometimes have a vascular strand in the nectary to assist in transport over a longer distance.{{cite journal |last1=Wallace |first1=Gary D. |title=Studies of the Monotropoideae (Ericaceae). Floral Nectaries: Anatomy and Function in Pollination Ecology |journal=American Journal of Botany |date=February 1977 |volume=64 |issue=2 |pages=199–206 |doi=10.1002/j.1537-2197.1977.tb15719.x |bibcode=1977AmJB...64..199W }}{{sfn|Rudall|2007|pages=96–98}}

Pollinators feed on the nectar and depending on the location of the nectary the pollinator assists in fertilization and outcrossing of the plant as they brush against the reproductive organs, the stamen and pistil, of the plant and pick up or deposit pollen.{{cite journal |last1=Heil |first1=Martin |title=Nectar: generation, regulation and ecological functions |journal=Trends in Plant Science |date=April 2011 |volume=16 |issue=4 |pages=191–200 |doi=10.1016/j.tplants.2011.01.003 |pmid=21345715 |s2cid=11206264 |doi-access=free |bibcode=2011TPS....16..191H }} Nectar from floral nectaries is sometimes used as a reward to insects, such as ants, that protect the plant from predators. Many floral families have evolved a nectar spur. These spurs are projections of various lengths formed from different tissues, such as the petals or sepals. They allow for pollinators to land on the elongated tissue and more easily reach the nectaries and obtain the nectar reward. Different characteristics of the spur, such as its length or position in the flower, may determine the type of pollinator that visits the flower.{{cite journal |last1=Pacini |first1=E. |last2=Nepi |first2=M. |last3=Vesprini |first3=J. L. |title=Nectar biodiversity: a short review |journal=Plant Systematics and Evolution |date=May 2003 |volume=238 |issue=1–4 |pages=7–21 |doi=10.1007/s00606-002-0277-y |bibcode=2003PSyEv.238....7P |s2cid=29016446 }}

Defense from herbivory is often one of the roles of extrafloral nectaries. Floral nectaries can also be involved in defense. In addition to the sugars found in nectar, certain proteins may also be found in nectar secreted by floral nectaries. In tobacco plants, these proteins have antimicrobial and antifungal properties and can be secreted to defend the gynoecium from certain pathogens.{{cite journal |last1=Thornburg |first1=R. W. |last2=Carter |first2=C. |last3=Powell |first3=A. |last4=Mittler |first4=R. |last5=Rizhsky |first5=L. |last6=Horner |first6=H. T. |title=A major function of the tobacco floral nectary is defense against microbial attack |journal=Plant Systematics and Evolution |date=May 2003 |volume=238 |issue=1–4 |pages=211–218 |doi=10.1007/s00606-003-0282-9 |bibcode=2003PSyEv.238..211T |s2cid=19339791 }}

Floral nectaries have evolved and diverged into the different types of nectaries due to the various pollinators that visit the flowers. In Melastomataceae, different types of floral nectaries have evolved and been lost many times. Flowers that ancestrally produced nectar and had nectaries may have lost their ability to produce nectar due to a lack of nectar consumption by pollinators, such as certain species of bees. Instead they focused on energy allocation to pollen production. Species of angiosperms that have nectaries use the nectar to attract pollinators that consume the nectar, such as birds and butterflies.{{cite journal |last1=Stein |first1=Bruce A. |last2=Tobe |first2=Hiroshi |title=Floral Nectaries in Melastomataceae and Their Systematic and Evolutionary Implications |journal=Annals of the Missouri Botanical Garden |date=1989 |volume=76 |issue=2 |pages=519–531 |id={{INIST|6608807}} |doi=10.2307/2399498 |jstor=2399498 |bibcode=1989AnMBG..76..519S |url=https://www.biodiversitylibrary.org/part/5356 }} In Bromeliaceae, septal nectaries (a form of gynoecial nectary) are common in species that are insect or bird pollinated. In species that are wind pollinated, nectaries are often absent because there is no pollinator.{{cite journal |last1=Sajo |first1=M. G. |last2=Rudall |first2=P. J. |last3=Prychid |first3=C. J. |title=Floral anatomy of Bromeliaceae, with particular reference to the evolution of epigyny and septal nectaries in commelinid monocots |journal=Plant Systematics and Evolution |date=August 2004 |volume=247 |issue=3–4 |page=215 |doi=10.1007/s00606-002-0143-0 |bibcode=2004PSyEv.247..215S |s2cid=20457047 }} In flowers that are generally pollinated by a long-tongued organism such as certain flies, moths, butterflies, and birds, nectaries in the ovaries are common because they are able to reach the nectar reward when pollinating. Sepal and petal nectaries are often more common in species that are pollinated by short-tongued insects that cannot reach so far into the flower.{{cite journal |last1=Rudall |first1=Paula J. |last2=Manning |first2=John C. |last3=Goldblatt |first3=Peter |title=Evolution of Floral Nectaries in Iridaceae |journal=Annals of the Missouri Botanical Garden |date=2003 |volume=90 |issue=4 |pages=613–631 |doi=10.2307/3298546 |jstor=3298546 |bibcode=2003AnMBG..90..613R |url=https://www.biodiversitylibrary.org/part/10182 }}

Nectar secretion increases as the flower is visited by pollinators. After pollination, the nectar is frequently reabsorbed into the plant.{{sfn|Thornburg|2001}} The amount of nectar in flowers at any given time is variable due to many factors, including flower age,{{Cite journal |last=Corbet |first=Sarah A. |date=2003-01-01 |title=Nectar sugar content: estimating standing crop and secretion rate in the field |journal=Apidologie |language=en |volume=34 |issue=1 |pages=1–10 |doi=10.1051/apido:2002049 |issn=0044-8435|doi-access=free }} plant location,{{Cite journal |last1=Pleasants |first1=John M. |last2=Zimmerman |first2=Michael |date=1979-08-01 |title=Patchiness in the dispersion of nectar resources: Evidence for hot and cold spots |url=https://doi.org/10.1007/BF00377432 |journal=Oecologia |language=en |volume=41 |issue=3 |pages=283–288 |doi=10.1007/BF00377432 |pmid=28309765 |bibcode=1979Oecol..41..283P |s2cid=41950102 |issn=1432-1939|url-access=subscription }} and habitat management.{{Cite journal |last1=Geest |first1=Emily A. |last2=Baum |first2=Kristen A. |date=2022 |title=The Impact of Fire on Nectar Quality and Quantity for Insect Pollinator Communities |url=https://bioone.org/journals/the-american-midland-naturalist/volume-187/issue-2/0003-0031-187.2.268/The-Impact-of-Fire-on-Nectar-Quality-and-Quantity-for/10.1674/0003-0031-187.2.268.full |journal=The American Midland Naturalist |volume=187 |issue=2 |pages=268–278 |doi=10.1674/0003-0031-187.2.268 |s2cid=248300845 |issn=0003-0031|url-access=subscription }}

{{See also|Myrmecophily|Plant defenses against herbivory}}

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Extrafloral nectaries (also known as extranuptial nectaries) are specialised nectar-secreting plant glands that develop outside of flowers and are not involved in pollination, generally on the leaf or petiole (foliar nectaries) and often in relation to the leaf venation.{{sfn|Rudall|2007|pages=66–68}}{{Cite journal | last1 = Heil | first1 = M.| last2 = Fiala | first2 = B.| last3 = Baumann | first3 = B. | last4 = Linsenmair | first4 = K.E. | title = Temporal, spatial and biotic variations in extrafloral nectar secretion by Macaranga tanarius | doi = 10.1046/j.1365-2435.2000.00480.x | journal = Functional Ecology | volume = 14 | issue = 6 | pages = 749 | year = 2000 | bibcode = 2000FuEco..14..749M| doi-access = }} They are highly diverse in form, location, size, and mechanism. They have been described in virtually all above-ground plant parts—including stipules, cotyledons, fruits, and stems, among others. They range from single-celled trichomes to complex cup-like structures that may or may not be vascularized. Like floral nectaries, they consist of groups of glandular trichomes (e.g., Hibiscus spp.) or elongated secretory epidermal cells. The latter are often associated with underlying vascular tissue. They may be associated with specialised pockets (domatia), pits or raised regions (e.g., Euphorbiaceae). The leaves of some tropical eudicots (e.g., Fabaceae) and magnoliids (e.g., Piperaceae) possess pearl glands or bodies which are globular trichomes specialised to attract ants. They secrete matter that is particularly rich in carbohydrates, proteins and lipids.{{sfn|Rudall|2007|pages=66–68}}{{Cite journal | last1 = Weber | first1 = M. G. | last2 = Keeler | first2 = K. H. | title = The phylogenetic distribution of extrafloral nectaries in plants | doi = 10.1093/aob/mcs225 | journal = Annals of Botany | year = 2012 | pmid = 23087129| pmc = 3662505| volume=111 | issue = 6 | pages=1251–1261}}{{Cite web |title=World List of Plants with Extrafloral Nectaries |url=http://www.extrafloralnectaries.org}}

File:Ants on Drynaria.jpgs on extrafloral nectaries in the lower surface of a young Drynaria quercifolia frond]]

While their function is not always clear, and may be related to regulation of sugars, in most cases they appear to facilitate plant insect relationships.{{sfn|Rudall|2007|pages=66–68}} In contrast to floral nectaries, nectar produced outside the flower generally has a defensive function. The nectar attracts predatory insects which will eat both the nectar and any plant-eating insects around, thus functioning as "bodyguards".[http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=0521819415 Plant-Provided Food for Carnivorous Insects – Cambridge University Press] Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly some species of ants and wasps, which have been observed to defend the plants bearing them. Acacia is one example of a plant whose nectaries attract ants, which protect the plant from other insect herbivores.{{sfn|Rudall|2007|pages=66–68}} Among passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs.{{cite web|last=Sezen|first=Uzay|title=Ants defending extrafloral nectaries of the passion flower (Passiflora incarnata)|url=http://vimeo.com/34448448|access-date=6 January 2012}} In many carnivorous plants, extrafloral nectaries are also used to attract insect prey.Merbach, M. 2001. Nectaries in Nepenthes. In: C.M. Clarke Nepenthes of Sumatra and Peninsular Malaysia. Natural History Publications (Borneo), Kota Kinabalu.{{pn|date=December 2023}}

File:Loxura atymnus-Kadavoor-2018-06-18-001.jpg butterflies and yellow crazy ants consuming nectar secreted from the extrafloral nectaries of a Spathoglottis plicata bud]]

Charles Darwin understood that extrafloral nectar "though small in quantity, is greedily sought by insects" but believed that "their visits do not in any way benefit the plant".{{Cite journal | last1 = Mancuso | first1 = S. | title = Federico Delpino and the foundation of plant biology | doi = 10.4161/psb.5.9.12102 | journal = Plant Signaling & Behavior | volume = 5 | issue = 9 | pages = 1067–1071 | year = 2010 | pmid = 21490417| pmc = 3115070| bibcode = 2010PlSiB...5.1067M }} Instead, he believed that extrafloral nectaries were excretory in nature (hydathodes). Their defensive functions were first recognized by the Italian botanist Federico Delpino in his important monograph Funzione mirmecofila nel regno vegetale (1886). Delpino's study was inspired by a disagreement with Darwin, with whom he corresponded regularly.

Extrafloral nectaries have been reported in over 3941 species of vascular plants belonging to 745 genera and 108 families, 99.7% of which belong to flowering plants (angiosperms), comprising 1.0 to 1.8% of all known species. They are most common among eudicots, occurring in 3642 species (of 654 genera and 89 families), particularly among rosids which comprise more than half of the known occurrences. The families showing the most recorded occurrences of extrafloral nectaries are Fabaceae, with 1069 species, Passifloraceae, with 438 species, and Malvaceae, with 301 species. The genera with the most recorded occurrences are Passiflora (322 species, Passifloraceae), Inga (294 species, Fabaceae), and Acacia (204 species, Fabaceae). Other genera with extrafloral nectaries include Salix (Salicaceae), Prunus (Rosaceae) and Gossypium (Malvaceae).

File:Nylanderia flavipes extrafloral nectary.jpg ant visiting extrafloral nectaries of Senna]]

Foliar nectaries have also been observed in 101 species of ferns belonging to eleven genera and six families, most of them belonging to Cyatheales (tree ferns) and Polypodiales.{{Cite journal |last1=Mehltreter |first1=Klaus |last2=Tenhaken |first2=Raimund |last3=Jansen |first3=Steven |date=2022 |title=Nectaries in ferns: their taxonomic distribution, structure, function, and sugar composition |url=https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1781 |journal=American Journal of Botany |language=en |volume=109 |issue=1 |pages=46–57 |doi=10.1002/ajb2.1781 |pmid=34643269 |issn=0002-9122}} Fern nectaries appear to have evolved around 135 million years ago, nearly simultaneously with angiosperms. However, fern nectaries did not diversify remarkably until nearly 100 million years later, in the Cenozoic, with weak support for a role played by arthropod herbivore diversifications.{{Cite journal |last1=Suissa |first1=Jacob S. |last2=Li |first2=Fay-Wei |last3=Moreau |first3=Corrie S. |date=2024-05-24 |title=Convergent evolution of fern nectaries facilitated independent recruitment of ant-bodyguards from flowering plants |journal=Nature Communications |language=en |volume=15 |issue=1 |pages=4392 |doi=10.1038/s41467-024-48646-x |issn=2041-1723|doi-access=free |pmid=38789437 |pmc=11126701 |bibcode=2024NatCo..15.4392S }}{{Cite journal |last1=Suissa |first1=Jacob S. |last2=Li |first2=Fay-Wei |last3=Moreau |first3=Corrie S. |date=2024-05-24 |title=Convergent evolution of fern nectaries facilitated independent recruitment of ant-bodyguards from flowering plants |journal=Nature Communications |language=en |volume=15 |issue=1 |page=4392 |doi=10.1038/s41467-024-48646-x |issn=2041-1723 |pmc=11126701 |pmid=38789437|bibcode=2024NatCo..15.4392S }} They are absent in bryophytes, gymnosperms, early angiosperms, magnoliids, and members of Apiales among the eudicots. Phylogenetic studies and the wide distribution of extrafloral nectaries among vascular plants point to multiple independent evolutionary origins of extrafloral nectaries in at least 457 independent lineages.

The main ingredients in nectar are sugars in varying proportions of sucrose, glucose, and fructose.{{cite journal|last1=Chalcoff|first1=Vanina|title=Nectar Concentration and Composition of 26 Species from the Temperate Forest of South America|journal=Annals of Botany|date=March 2006|volume=97|issue=3|pages=413–421|doi=10.1093/aob/mcj043|pmc=2803636|pmid=16373370}} In addition, nectars have diverse other phytochemicals serving to both attract pollinators and discourage predators.{{cite journal|pmc=2802787|year=2009|last1=González-Teuber|first1=M.|title=Nectar chemistry is tailored for both attraction of mutualists and protection from exploiters|journal=Plant Signaling & Behavior|volume=4|issue=9|pages=809–813|last2=Heil|first2=M.|pmid=19847105|doi=10.4161/psb.4.9.9393|bibcode=2009PlSiB...4..809G }}{{sfn|Nicolson et al|2017}} Carbohydrates, amino acids, and volatiles function to attract some species, whereas alkaloids and polyphenols appear to provide a protective function.

The Nicotiana attenuata, a tobacco plant native to the US state of Utah, uses several volatile aromas to attract pollinating birds and moths. The strongest such aroma is benzylacetone, but the plant also adds bitter nicotine, which is less aromatic, so may not be detected by the bird until after taking a drink. Researchers speculate the purpose of this addition is to discourage the forager after only a sip, motivating it to visit other plants, therefore maximizing the pollination efficiency gained by the plant for a minimum nectar output.{{sfn|Nicolson et al|2017}}{{cite news |last1=Everts |first1=Sarah |title=Two-Faced Flowers |url=https://cendevqa.acs.org/articles/86/i35/Two-Faced-Flowers.html |work=Chemical & Engineering News |date=1 September 2008 }} Neurotoxins such as aesculin are present in some nectars such as that of the California buckeye.[http://www.globaltwitcher.com/artspec_info.asp?thingid=82383 C.Michael Hogan (2008) Aesculus californica, Globaltwitcher.com, ed. N. Stromberg] Nectar contains water, essential oils, carbohydrates, amino acids, ions, and numerous other compounds.{{sfn|Thornburg|2001}}{{sfn|Nicolson et al|2017}}{{sfn|Park |Thornburg|2009}}

Some insect pollinated plants lack nectaries, but attract pollinators through other secretory structures. Elaiophores are similar to nectaries but are oil secreting. Osmophores are modified structural structures that produce volatile scents. In orchids, these have pheromone qualities. Osmophores have thick domed or papillate epidermis and dense cytoplasm. Platanthera bifolia produces a nocturnal scent from the labellum epidermis. Ophrys labella have dome-shaped, papillate, dark-staining epidermal cells forming osmophores. Narcissus emit pollinator specific volatiles from the corona.{{sfn|Rudall|2007|pages=96–98}}

• Nectar guide
• Nectar source
• Nectarivore
• Northern American nectar sources for honey bees

{{Reflist}}

{{refbegin|30em}}

;Books

• Baker, H.G. and Baker, I. (1975) Studies of nectar-constitution and pollinator-plant coevolution. In Coevolution of animals and plants. Gilbert, L.E. and Raven, P.H. ed. Univ. of Texas Press, Austin, 100–140.
• Esau, K. (1977) Anatomy of seed plants. John Wiley & Sons, New York.
• {{Cite book|editor-last1=Nicolson|editor-first1=Susan W.|editor-last2=Nepi|editor-first2= Massimo|editor-last3=Pacini|editor-first3=Ettore|url=https://books.google.com/books?id=0L1cTNozMw8C|title=Nectaries and Nectar| publisher= Springer Publications|location=Dordrecht|year= 2007 |isbn=978-1-4020-5937-7|ref={{harvid|Nicolson et al|2017}}}}
• Roshchina, V.V. and Roshchina, V.D. (1993) The excretory function of higher plants. Springer-Verlag, Berlin.
• {{cite book |last1=Rudall |first1=Paula J. |author-link=Paula Rudall |title=Anatomy of Flowering Plants: An Introduction to Structure and Development |date=2007 |publisher=Cambridge University Press |isbn=978-1-139-45948-8 }}

;Articles

• {{cite journal | last1 = Baker | first1 = H.G. | last2 = Baker | first2 = I. | year = 1973 | title = Amino acids in nectar and their evolutionary significance | journal = Nature | volume = 241 | issue = 5391| pages = 543–545 | doi=10.1038/241543b0| bibcode = 1973Natur.241..543B | s2cid = 4298075 }}
• Baker, H.G. and Baker, I. (1981) Chemical constituents of nectar in relation to pollination mechanisms and phylogeny. In Biochemical aspects of evolutionary biology. 131–171.
• Beutler, R. (1935) Nectar. Bee World 24:106–116, 128–136, 156–162.
• {{cite journal | last1 = Burquez | first1 = A. | last2 = Corbet | first2 = S.A. | year = 1991 | title = Do flowers reabsorb nectar? | journal = Funct. Ecol. | volume = 5 | issue = 3| pages = 369–379 | doi=10.2307/2389808| jstor = 2389808 | bibcode = 1991FuEco...5..369B }}
• {{cite journal | last1 = Carter | first1 = C. | last2 = Graham | first2 = R. | last3 = Thornburg | first3 = R.W. | year = 1999 | title = Nectarin I is a novel, soluble germin-like protein expressed in the nectar of Nicotiana sp. | journal = Plant Mol. Biol. | volume = 41 | issue = 2| pages = 207–216 | doi = 10.1023/A:1006363508648 | pmid = 10579488 | s2cid = 18327851 }}
• {{cite journal | last1 = Deinzer | first1 = M.L. | last2 = Tomson | first2 = P.M. | last3 = Burgett | first3 = D.M. | last4 = Isaacson | first4 = D.L. | year = 1977 | title = Pyrrolizidine alkaloids: Their occurrence in honey from tansy ragwort (Senecio jacobaea L.) | journal = Science | volume = 195 | issue = 4277| pages = 497–499 | doi=10.1126/science.835011| pmid = 835011 | bibcode = 1977Sci...195..497D }}
• {{cite journal | last1 = Ecroyd | first1 = C.E. | last2 = Franich | first2 = R.A. | last3 = Kroese | first3 = H.W. | last4 = Steward | first4 = D. | year = 1995 | title = Volatile constituents of Dactylanthus taylorii flower nectar in relation to flower pollination and browsing by animals | journal = Phytochemistry | volume = 40 | issue = 5| pages = 1387–1389 | doi=10.1016/0031-9422(95)00403-t| bibcode = 1995PChem..40.1387E }}
• {{cite journal |last1=Ferreres |first1=Federico |last2=Andrade |first2=Paula |last3=Gil |first3=Maria I. |last4=Tomás-Barberán |first4=Francisco A. |title=Floral nectar phenolics as biochemical markers for the botanical origin of heather honey |journal=Zeitschrift für Lebensmittel-Untersuchung und Forschung |date=1996 |volume=202 |issue=1 |pages=40–44 |doi=10.1007/BF01229682 |s2cid=84713582 }}
• Frey-Wyssling, A. (1955) The phloem supply to the nectaries. Acta Bot. Neerl. 4:358–369.
• {{cite journal | last1 = Griebel | first1 = C. | last2 = Hess | first2 = G. | year = 1940 | title = Der C-Vitamingehalt des Blütennektars bestimmter Labiaten| journal = Zeitschrift für Untersuchung der Lebensmittel| volume = 79 | issue = 1–2 | pages = 168–171 | doi = 10.1007/BF01662427 }}
• {{cite journal | last1 = Heinrich | first1 = G | year = 1989 | title = Analysis of cations in nectars by means of a laser microprobe mass analyser (LAMMA) | journal = Beitr. Biol. Pflanz | volume = 64 | pages = 293–308 }}
• {{cite journal | last1 = Heslop-Harrison | first1 = Y. | last2 = Knox | first2 = R.B. | year = 1971 | title = A cytochemical study of the leaf-gland enzymes of insectivorus plants of the genusPinguicula | journal = Planta | volume = 96 | issue = 3| pages = 183–211 | doi=10.1007/bf00387439| pmid = 24493118 | bibcode = 1971Plant..96..183H | s2cid = 24535933 }}
• {{cite journal |last1=Jeiter |first1=Julius |last2=Hilger |first2=Hartmut H |last3=Smets |first3=Erik F |last4=Weigend |first4=Maximilian |title=The relationship between nectaries and floral architecture: a case study in Geraniaceae and Hypseocharitaceae |journal=Annals of Botany |date=November 2017 |volume=120 |issue=5 |pages=791–803 |doi=10.1093/aob/mcx101|pmid=28961907 |pmc=5691401 |ref={{harvid|Jeiter et al|2017}}}}
• {{cite journal |last1=Park |first1=Sanggyu |last2=Thornburg |first2=Robert W. |title=Biochemistry of Nectar Proteins |journal=Journal of Plant Biology |date=27 January 2009 |volume=52 |issue=1 |pages=27–34 |doi=10.1007/s12374-008-9007-5 |bibcode=2009JPBio..52...27P |s2cid=9157748 }}
• {{cite journal | last1 = Peumans | first1 = W.J. | last2 = Smeets | first2 = K. | last3 = Van Nerum | first3 = K. | last4 = Van Leuven | first4 = F. | last5 = Van Damme | first5 = E.J.M. | year = 1997 | title = Lectin and alliinase are the predominant proteins in nectar from leek (Allium porrum L.) flowers | journal = Planta | volume = 201 | issue = 3| pages = 298–302 | doi=10.1007/s004250050070| pmid = 9129337 | bibcode = 1997Plant.201..298P | s2cid = 28957910 }}
• {{cite journal |last1=Rodríguez-Arce |first1=Angel L. |last2=Díaz |first2=Noemi |title=THE STABILITY OF β-CAROTENE IN MANGO NECTAR |journal=The Journal of Agriculture of the University of Puerto Rico |date=April 1992 |volume=76 |issue=2 |pages=101–102 |doi=10.46429/jaupr.v76i2.4139 |s2cid=247606388 |doi-access=free }}
• {{cite journal | last1 = Scala | first1 = J. | last2 = Iott | first2 = K. | last3 = Schwab | first3 = W. | last4 = Semersky | first4 = F.E. | year = 1969 | title = Digestive secretion of Dionaea muscipula (Venus's-Flytrap) | journal = Plant Physiol | volume = 44 | issue = 3| pages = 367–371 | doi=10.1104/pp.44.3.367| pmid = 16657071 | pmc = 396093 }}
• {{cite journal | last1 = Smith | first1 = L.L. | last2 = Lanza | first2 = J. | last3 = Smith | first3 = G.C. | year = 1990 | title = Amino acid concentrations in extrafloral nectar of Impatiens sultani increase after simulated herbivory | journal = Ecol. Publ. Ecol. Soc. Am. | volume = 71 | issue = 1| pages = 107–115 | doi=10.2307/1940251| jstor = 1940251 | bibcode = 1990Ecol...71..107S }}
• Vogel, S. (1969) Flowers offering fatty oil instead of nectar. Abstracts XIth Internatl. Bot. Congr. Seattle.

;Websites

• {{cite web |last1=Thornburg |first1=Robert |title=Nectar |url=http://www.bb.iastate.edu/necgex/Nectar.htm |website=Nectary Gene Expression Index. |publisher=Department of Biochemistry, Biophysics and Molecular Biology,Iowa State University |access-date=11 January 2020 |archive-url=https://web.archive.org/web/20030910162730/http://www.bb.iastate.edu/necgex/Nectar.htm |archive-date=10 September 2003|date=4 June 2001}}

{{refend}}

{{Commons category|Nectar}}

• [https://web.archive.org/web/20140323210940/http://en.lamieldeabejas.com/la-miel.html Overview and summary of the honey bee (and Nectar) information. (News, Economy, Trade, Problems, etc)]
• [http://cubits.org/hummingbirdgardening/db/hummingbirdplants/index.php Hummingbird Plants Database] {{Webarchive|url=https://web.archive.org/web/20110725213745/http://cubits.org/hummingbirdgardening/db/hummingbirdplants/index.php |date=25 July 2011 }}

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