Floral Scent: Where? Why? How Long?

I’ve been thinking about flowers and their scent recently. It’s sent me on a search through the internet and I’ve found some interesting facts about flowers and their scent.

A lot of flowers today have little or no scent, especially those that you find in flower shops. Over the years breeders have focused on size, color, longevity and other factors but scent was not one of them. As a result, most of the flowers that are shipped around the world have lost their scent since this wasn’t a factor in their breeding and selection.

IMG_3000The purpose of scent is to attract pollinators. (Many of the flowers grown today for the floral industry and for the garden are cloned plants so once again, the scent isn’t needed and it’s loss isn’t a problem.) But in nature, plants that are pollinated by bees or butterflies tend to have a light scent that’s strongest in the day. Those pollinated by moths often have a strong scent that intensifies at night. There are also some flowers like the corpse plant (Amorphophallus titanum) that are pollinated by flies and the smell they exude is one of rotting meat – needless to say these have never caught on as garden flowers!

I understand why flowers have or once had a scent but where’s the origin of the smell? I’d always assumed that it was somewhere deep inside the flower. It took a lot of hunting on the net but I found a couple of articles by Natalia Dudareva from Purdue that address some research being done on scent.

bee and sageWhat amazed me was that the scent of most flowers come from their petals – I never knew that. Floral fragrances start as volatile oils that are produced in the petals. Flowers might have as few as seven or eight different oils or as many as 100. The combination leads to the unique scent of each flower and the volatile nature of these chemicals allow them to reach the antennae of insects as well as our noses.

There’s another interesting insight from Dudareva’s research. The purpose of scent is to attract pollinators so that the flower can set seed. However, she noted that in snapdragons (Antirrhinum majus), the scent being released by the flower decreases when the flower is fertilized.

In snapdragons, once pollen is placed on the stigma of the pistil (the female organ within the flower), it takes about two days for the pollen to grow a tube that reaches into the ovary of the flower and fertilizes the ovum. During this time the flower still produces scent since there’s no guarantee that the pollen will make a successful fertilization. So the plant keeps attracting pollinators by exuding a scent, making sure that pollen keeps being brought to the flower. But when the flower is fertilized, the scent lessens.

This just boggles my mind and confirms for me that plants are amazing! That a flower can attract pollinators when it needs them and stop attracting them once they’ve served their purpose is a pretty advanced way of interacting with the world.

From now on I’m going to be a more aware of the scents of flowers. I’m going to be more conscious of petals and the oils that they’re producing. I’m going to notice what time of day flowers smell their best. And I’m going to keep my nose attuned to when a flower stops smelling. When it does, it just might be that the scent has served it’s purpose and an embryonic seed may have started to form.

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2 responses to “Floral Scent: Where? Why? How Long?

  1. Fascinating! Thank you for this. I think other scents used by plants can be to deter insects, for examples herbs like rosemary or sage have oils in the leaves, mint is especially good for keeping flies away. I’m not sure how that works with the flowers though, do mint leaves lose their scent when the plant is flowering? Or do the flowers attract different ones to those that are repelled? I think I need to do some investigating of my own…

    • Thanks for your comments. There are scents in leaves and you’re right, they’re often for repelling insects.They’re produced by the leaves so it’s a different process from attracting pollinators.
      But it is interesting that it’s often recommended to harvest herbs before the flowers open.
      Good luck with your investigation and I’ll be doing some thinking about it as well.
      Marc

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