Why a sunflower is actually a hippy commune
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.
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.
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.
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!
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.