Nectar

 ( Flowers ) 

• 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)

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. Nectar from floral nectaries is sometimes used as a reward to insects, such as , 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.

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 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.

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 . 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 and butterflies. 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. In flowers that are generally pollinated by a long-tongued organism such as certain flies, , 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.

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. 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 herbivore insects around, thus functioning as "bodyguards". Plant-Provided Food for Carnivorous Insects – Cambridge University Press Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly some species of and , 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. Among Passiflora, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs. 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.

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". Instead, he believed that extrafloral nectaries were Excretion in nature (). Their defensive functions were first recognized by the Italian people 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 belonging to 745 genus and 108 families, 99.7% of which belong to (angiosperms), comprising 1.0 to 1.8% of all known species. They are most common among , 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).

Foliar nectaries have also been observed in 101 species of belonging to eleven genera and six families, most of them belonging to Cyatheales (tree ferns) and Polypodiales. 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. They are absent in , , early , magnoliids, and members of Apiales among the eudicots. Phylogenetic studies and the wide distribution of extrafloral nectaries among vascular plants point to multiple independent origins of extrafloral nectaries in at least 457 independent lineages.