More to dandelions than meets the eye

Many readers will know that I am a taraxaphile, I love the species Taraxacum, the dandelions. The bright yellow flower heads brighten a spring day, they feed more than a hundred different invertebrates including butterflies and bees, and they present an intriguing puzzle to people trying to catalogue the nature around us.

Given a cursory glance, especially by gardeners, all dandelions look the same, but a closer look shows they actually come in a bewildering range of shapes and sizes. Some are less than 3cm across, some are much larger, some spread their leaf rosette flat, others have leaves that stand upright. The leaves themselves have almost as many patterns as snowflakes, plain with a few lobes to many frilly lobes.

Most nature recorders used to lump all dandelions together as the common dandelion with the scientific name Taraxacum officinale. Recent science looking at the genetics of these different shapes and sizes has shown that they are actually separate species, over 200 of them.

Many flowers have mechanisms to prevent inbreeding by keeping their pollen and ovules separate. Dandelions go one step further, they produce fertile seeds directly without the need for pollination. The scientific word for this is apomixis, literally away from mixing. Dandelions are generous to pollinating insects, but this is a hangover from long ago, they do not need the help of pollinators.

It is this apomixis that has led to so many different dandelions. Those of you familiar with Charles Darwin will know that living things evolve slowly over time. Very briefly, as small changes are brought about by random mutations, if they give an advantage those individuals have more success in breeding and the change spreads out through the whole population as males and females mix their chromosomes in reproduction.

Over time individual dandelions will have undergone single mutations. Some will have resulted in that dandelion being the end of the line but, if the dandelion survives, there will be no mixing up with genes from other plants and so a new breeding line will be established. This process will have worked through many times and the surviving mutants have evolved into different species that keep themselves apart from the others.

Different breeding lines will have had more or less success in different habitats, some do well in the mountains, some do well in pastures, others do well in regularly mown lawns. There is even one species that survives happily in sand dunes, Taraxacum stenoglossum.

We have at least 6 different dandelion species around the town. As you walk about or work in your garden, take a moment to have a closer look. Apart from size, look at the leaf shape and the colour of the midrib, some are green, some white, others pink or purple. Do they lie flat or stand up? One thing that very few people notice is the rings of bracts under the flower head, some stand out like a choirboy’s collar, others stand upright clasping the stem. Some are grey, others purple.

A say flower head because a dandelion is not a single flower but a cluster of tiny florets, each one a fully formed flower in its own right. What look like single petals are ligules made from five petals fused together, you can see the five teeth at the tip. In some species the ligules are pure yellow, some have red or grey stripes on the outside, others have red teeth at the tip.

Dandelions are fascinating and reward inquisitive people who make a closer inspection. More importantly, they make a great contribution to the web of nature that keeps us alive, give them some space and time to do their thing.

Ed Dolphin