Nature Notes – Dandelions by Ian Brand

What do Dandelions and Bananas have in common, apart from both being yellow?

If being a naturalist were a religion, then spring would be our Christmas, and if spring had a colour, that would be yellow. I always look forward to the seasonal quintet of Lesser Celandine, Cowslip, Primrose, Daffodil and not forgetting the humble Dandelion as it brightens our grass verges.  Dandelions (Taraxacaum agg) are loathed by gardeners and ignored by naturalists. Look again either at a single bloom or a field covered in yellow; it is beautiful. If this were a rare plant, horticulturists and botanists would travel miles to see it. Poor Victorian cottage gardeners would often nurture a few cherished Dandelions to brighten their garden.

I am here to change your mind about the Dandelion. It is often the common plants which have the most interesting stories and fascinating biology. Take that unusual name ‘Dandelion’ – it is a corruption of the French ‘Dent de lion’ – Lion’s tooth. Place two leaves parallel, side by side and you will see what I mean. The French have their own name, ‘Piss en lit’ – ‘wet the bed’ due to its diuretic effect if eaten in large quantities. However, don’t let that put you off trying a few fresh young Dandelion leaves in a salad as an alternative to those expensive bags of peppery Rocket.

I keep referring to it as a flower, but strictly, botanically speaking it is a flower head or inflorescence, made of many small flowers or florets. Although it does not look much like a Daisy, it is a member of the Daisy family (Asteraceae), previously known as Compositae after the flower head which is a composite of small florets. Our common garden lawn Daisy has two types of florets: outer white ray (lingulate) florets, and inner yellow disc (tubular) florets. Dandelions are composed just of ray florets, while Thistles (another family member) consist solely of disc florets, which is why neither have that typical Daisy-like appearance.

If the individual flower or floret is very small as in Dandelion, it makes sense to bunch them together to form a composite flower, making a perfect landing platform for insects. Members of the Carrot family do just the same - think of Hogweed, its umbel of small flowers is like an insect airport on a hot summer’s day, with insects continuously flying in and out.

Now that conundrum; what do Dandelions and Bananas have in common, apart from being yellow? The answer, they both have three sets of chromosomes. Time for some simplified genetics. All mammals including of course humans have just two sets of chromosomes. Plants are often the same, but there are many which have multiple sets (Polyploidy). This includes many of our food plants. Peanuts have four sets, Wheat six and Strawberries eight.

Having multiple sets is not a problem if it is an even number. If you have an odd number like three, when it comes to producing the female ova (egg) or male pollen, you need to halve the number of chromosomes, but two into three is one and half, which just doesn’t work and results in infertility and non-viable seed is produced. This is why the commonly eaten Cavendish Banana is either seedless or has very small non-viable black seeds.

Now the brainteaser, Dandelions also have three sets of chromosomes and therefore should be sterile. But, as every young child knows blowing on a Dandelion clock it has multiple fertile seeds, each with its own feathery parachute.

Dandelions produce viable seed by a complex genetic process called ‘Apomixis’. Seed is produced without the need for fertilization, directly from the female tissue in the ovary, no need for male pollen. Think of it a bit like ‘Virgin Birth’. That raises another question – then why do insects visit Dandelions for pollen? This takes large amounts of the plant’s energy to produce. The answer to that question is even more complicated, you will just have to take my word. It is an important first step in initiating the whole apomixic process. Hopefully your thoughts about what many people regard as common weed have now changed. Not only does it have a ‘pretty face’, but it is clever too!