I'm starting this series because I am in some amazing plant groups, and I have learned so much about what to research just by listening to suggestions that people provide after someone posts about a plant with a problem. Not everyone is so lucky to have a local, knowledgable community to refer to when they have issues or questions- so I thought I'd make a place here. Hopefully, this will help some of you who are finding strange things on your plant figure out what it is!
Today I am going to dive into extrafloral nectaries- something you might have never even heard of until just now!
What are extrafloral nectaries (EFN)? Let's break it down:
noun BOTANY plural noun: nectaries
a nectar-secreting glandular organ in a flower (floral) or on a leaf or stem (extrafloral).
As explained by the Oxford dictionary of languages, nectaries are "nectar-secreting glandular organs" on plants. If the plant flowers, it has floral nectaries, if it doesn't it may have extrafloral nectaries. If you have a philodendron, it might have some of these little glands and may or may not actively secrete nectar in your home. Some other plants also have extrafloral nectaries, but it is not found on all plants. For a compilation of the species that do, check out this site.
The glands secreting sugary nectar could be confused with guttation or transpiration (different ways plants release excess water) but are very different! For more on those wacky plant phenomena, I'll make a post later in the series.
So why do these plants produce this nectar anyway?
The abstract from this article on Mechanical defenses of plant extrafloral nectaries against herbivory from the NCBI does a great job condensing a few basics on the subject:
"Extrafloral nectaries play an important role in plant defense against herbivores by providing nectar rewards that attract ants and other carnivorous insects. However, extrafloral nectaries can themselves be targets of herbivory, in addition to being exploited by nectar-robbing insects that do not provide defensive services. We recently found that the extrafloral nectaries of Vicia faba plants, as well as immediately adjacent tissues, exhibit high concentrations of chemical toxins, apparently as a defense against herbivory. Here we report that the nectary tissues of this plant also exhibit high levels of structural stiffness compared to surrounding tissues, likely due to cell wall lignification and the concentration of calcium oxalate crystals in nectary tissues, which may provide an additional deterrent to herbivore feeding on nectary tissues."
The nectar that is secreted from the extrafloral nectaries is actually used to attract other organisms (as far as I have been able to find, they serve almost entirely to attract ants) that are beneficial to the plant's health and wellbeing. The ants get the sugary nectar from the plant which sustains them and in turn, the ants provide some protection from other organisms and herbivores that may want to eat the plant or cause it harm. This is an example of plant-insect mutualism, where the two organisms work together to provide a win-win scenario where each party benefits (isn't nature the COOLEST?!). Alternatively, the nectar can also attract predators or other beings that take the substance without reciprocating or damage the plant altogether- some plants have been found to secrete different substances from their nectaries that are toxic to insects which is also noted in the article referenced above.
Whatever is coming out of your plant from these organs, it is totally natural and is not going to hurt your plant. Although the nectaries can attract pests, they are not themselves, pests, or something that needs to be removed from your plant. Here are some photos of extrafloral nectaries provided by fern.mama (who has an amazing collection you should check out on IG btw). She was curious about what was happening with her GORGEOUS Pastazanum when she found these little spots all over it. No pests found, and she thought it could be some form of guttation.
These glands have different forms, so if you have a plant with extrafloral nectaries, they might not look just like this, but be sure to consider that your plant may have these if it is one of the plants documented having EFN- especially before you go scraping or damaging the plant because you think these are pests!
If you'd like to learn more about extrafloral nectaries and if it's the weird thing on your plant, check out some of these resources:
The Daily Garden: Extrafloral Nectaries