Why a sunflower is actually a hippy commune

A microscopic view of a sunflower. Photo via Max Pixel.

Being a budding plant scientist, I’m frequently asked (once a year) what my favourite fun fact about plants is. There’s an abundance to choose from – trees can hear running water, signal to other trees that predators are approaching, and even send food to younger trees growing on the forest floor.

But the fact I always revert to is one about the humble sunflower. It’s something so simple that I felt somewhat silly that I hadn’t noticed it before, considering I do stalk flowers a lot. But that’s what made it so wonderful to learn.

The fact is, a single sunflower is not actually one flower, but hundreds. Hundreds of mini flowers housed in one super-structure that we know as the sunflower. Take a really close look and you’ll see them, the miniature flowers with their towering stigmas reaching out into the sky.

This is a sunflower, in case you had forgotten. Picture via Pixabay.

Get around the jargon

The sunflower as we know it is biologically a capitulum, which is botanical terminology for “flower head”. The mini flowers housed upon the structure are called florets, of which there are two types. The disc florets make up the brown mass in the centre of the sunflower, and the ray florets make up the ring of characteristic yellow petals on the outside.

Both serve different societal roles in the sunflower commune.

Close-up illustrations of a disc floret (left) and ray floret. While the disc floret resembles an elongated flower with perfect symmetry, the ray floret has its giant yellow petals fused on one side. Pictures via Wikimedia commons.

 

The ray florets are the tourism operators, working around the clock to attract pollinators to visit the commune. They are sexually sterile, unable to produce seed. However, they boast a bright yellow collection of fused petals, which act as billboards to attract commuting bees. The tips of the petals are particularly important as they reflect UV light, providing bees with long-distance cues for recognising the sunflower.

As the bees approach the sunflower, the base of the ray florets appear as flashy landing strips, directing the bees towards the flower head’s centre. Picture Times Square; there’s a lot of colourful, sparkly marketing going on here.

This brings us to the disc florets in the centre, which are sexually complete flowers – having both male and female parts. What’s a hippy commune without a good dose of love in the air? That’s what the disc florets are all about – a mass gathering of sexually active flowers congregated together in the centre of the flower head.

The sunflower in all its glory. The centre mass of disc florets is visible, with those on the edge in bloom. The florets toward the centre are closed but will soon open . A visiting bee feeds on nectar, depositing pollen as it walks. Picture via Pixnio.

 

And here’s the genius part: At any given time, most of the florets in the centre of the commune are releasing nectar and pollen, while the florets on the periphery are female-active and ready to receive pollen. As the bees walk across the flower head towards the nectar in the centre, they deposit pollen from other sunflowers they have visited onto the female florets as they go!

Evolution/10.

Not just sunflowers

Sunflowers aren’t the only flowers which turn out to be ‘flower heads’. So are daisies, calendulas, marigolds, gerberas, artichokes, dandelions and nearly 23,000 other species in the daisy family. To keen plant folk this flower family is referred to as the Asteraceae, and it happens to be the largest family of flowering plants there is. All have this characteristic capitula structure in common, with arrangements of ray and disc flowers.

So, sunflowers do have a great socialist reproductive strategy going on, but seems they aren’t all that unique after all.  

For more details at the micro-level, check out this journal paper.

 


10 Responses to “Why a sunflower is actually a hippy commune”

  1. Ashley Densham says:

    Thanks Chris, yeah I think a socialist analogy is generally a good one to employ when it comes to flowers and bees

  2. Ashley Densham says:

    Good point Gabrielle! Surely then a sunflower should have a higher weighting as a gift

  3. Alexander says:

    I’ve never heard anything like this, makes me want to plant some sun flowers!

  4. Jeremy Le says:

    Love your metaphors and imagery! I really didn’t know that about sunflowers and loved learning something new from this blog.

  5. Christopher Aitken says:

    Good writing, nice and clear and enough jargon to make me feel a bit wiser at the end. I like the fact about the ‘division or labour’ across the capitulum.

  6. Gabrielle Stinear says:

    So does that mean buying one sunflower is actually buying a giant bunch of flowers? Super interesting read!!

  7. Ashley Densham says:

    Awesome! Good to know the fun sunflower facts are spreading around. Thanks fellow horticulturalist 🙂

  8. Ashley Densham says:

    Thanks for the heads up David, should be resolved now. Glad you enjoyed.

  9. David Setyanugraha says:

    Interesting topic, Ashley!

    I only have one comment. I can’t see the second post image. The image says Pixabay, no hotlinking. Maybe, you can use another image.

  10. Jasmine Rhodes says:

    As a horticulturist who was just explaining this to someone the other day (to their amazement), I loved this post! It has a fun, enthusiastic tone and really demonstrates your passion for plants.

    From a fellow plant-lover 🙂