lots of prunus species have nectar producing glands on the leaf stalks a better pic would help
Extrafloral nectaries
See also:
Myrmecophily and
Plant defenses against herbivory
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.
[15][16] 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.
[15][17]

Extrafloral nectaries on the petiole of a wild cherry (
Prunus avium) leaf

Extrafloral nectaries on a red stinkwood (
Prunus africana) leaf
Ants 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.
[15] In contrast to floral nectaries, nectar produced outside the flower generally have a defensive function. The nectar attracts predatory insects which will eat both the nectar and any
plant-eating insects around, thus functioning as 'bodyguards'.
[18] 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.
[15][16] Among
passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs.
[19] In many
carnivorous plants, extrafloral nectaries are also used to attract insect
prey.
[20]
Loxura atymnus butterflies and
yellow crazy ants consuming nectar secreted from the extrafloral nectaries of a
Spathoglottis plicata bud
Nylanderia flavipes ant visiting extrafloral nectaries of
Senna
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".
[21] 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
Charles Darwin, with whom he corresponded regularly.
[21]
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).
[17] Other genera with extrafloral nectaries include
Salix (
Salicaceae),
Prunus (
Rosaceae) and
Gossypium (
Malvaceae).
[19]
Foliar nectaries have also been observed in 39 species of
ferns belonging to seven genera and four families of
Cyatheales and
Polypodiales.
[17] They are absent, however, in
bryophytes,
gymnosperms, early
angiosperms,
magnoliids, and members of
Apiales among the eudicots.
[17] 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.
[17]