Nectaries can occur on any floral part, but they may also represent a modified part or a novel structure. 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. 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.
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. 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.
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.
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.
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. In species that are wind pollinated, nectaries are often absent because there is no pollinator to provide a reward for. 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.
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.
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. Hibiscus spp.
The latter are often associated with underlying vascular tissue. They may be associated with specialised pockets domatia , pits or raised regions e. The leaves of some tropical eudicots e. Fabaceae and magnoliids e. 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. 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. The nectar attracts predatory insects which will eat both the nectar and any plant-eating insects around, thus functioning as 'bodyguards'. Acacia is one example of a plant whose nectaries attract ants, which protect the plant from other insect herbivores.
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". Their defensive functions were first recognized by the Italian botanist Federico Delpino in his important monograph Funzione mirmecofila nel regno vegetale Delpino's study was inspired by a disagreement with Charles Darwin , with whom he corresponded regularly.
Extrafloral nectaries have been reported in over species of vascular plants belonging to genera and families , They are most common among eudicots , occurring in species of 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 species, Passifloraceae , with species, and Malvaceae , with species.
The genera with the most recorded occurrences are Passiflora species, Passifloraceae , Inga species, Fabaceae , and Acacia species, Fabaceae. Foliar nectaries have also been observed in 39 species of ferns belonging to seven genera and four families of Cyatheales and Polypodiales. The main ingredients in nectar are sugars in varying proportions of sucrose , glucose , and fructose.
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.
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. From Wikipedia, the free encyclopedia. Sugar-rich liquid produced by many flowering plants, that attracts pollinators and insects.
For other uses, see Nectar disambiguation. See also: Myrmecophily and Plant defenses against herbivory. Extrafloral nectaries with droplets of nectar on the petiole of a wild cherry Prunus avium leaf. Extrafloral nectaries on a red stinkwood Prunus africana leaf.
Retrieved 17 January Online Etymology Dictionary, Douglas Harper. Retrieved 28 May Pollination and floral ecology. Princeton University Press, Botanical Gazette, vol. Floral nectaries: anatomy and function in pollination ecology. Nepi, and J. Rudall, and C. Manning, and Peter Goldblatt. Functional Ecology. Annals of Botany. PMC Operations Support Software Solutions Unlimited. Social Recognition. Seamless integrations with your other software Nectar connects with all your other tools to create a smooth experience.
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