Friday, 23 April 2010

Musical Carrots and More Floral Spots*



Standing in what is called the First Farm, the place where European style agriculture started in Australia, you can see coffee, bananas and sugar cane doing wonderfully today. As we’ve discussed before, the attempts of the first settlers weren’t always successful.

By the late eighteenth century vegetables and fruits were cultivated in lots of places around the world. They had already been selected to make them big and juicy, and a better food source (although even in those days breeding for longevity and beauty would have been important).

I've talked before about the tiny corn kernels of Teosinte from Mexico, in our Rare and Threatened Garden, and other grains. Today let’s talk carrots…

A breeder in the UK recently announced a new carrot cultivar called ‘Purple Haze’. Nothing to do with Jimi Hendrix, these carrots have a deep-purple (nothing to do with Deep Purple…) coloured outer layer. Simon has mentioned these before on radio.

In fact they are more like the original carrot, a purple or red tuber, reputedly bred by the Dutch in the seventeenth century to be bright orange in honour of William I, Prince of Orange. The name ‘carrot’ and its botanical species name ‘carota’ are both derived from a Celtic word meaning red.

‘Purple Haze’ is said to be sweeter than our common orange forms, which I doubt would have been the case with the original carrot.

And why were they purple or red in the first place? Perhaps to warn off insects. In deciduous trees, the leaves change colour in autumn as the chlorophyll is recycled - either yellow as a default, or red if a new pigment, anthocyanin, is produced. As I’ve explained before, anthocyanins may provide protection from sunburn or pests. Insects such as aphids are attracted by green but tend to avoid red. Maybe if the tuber sticks out of the ground at the top, a red colour fends off nasty bugs. Or perhaps it needs some sun protection.

Although Governor Phillip understood the importance of green vegetables in 1788, salad vegetables and fruits haven’t featured strongly in the English culinary tradition. Margaret Visser in her wonderful book Much Depends on Dinner notes that in the Middle Ages most were called ‘herbs’ or at best ‘worts’ (greens), and were a poor second to meats and pastries. Vegetables were probably mostly for the poor.

As an aside, and back to botany for a moment, the flowering head of the Wild Carrot always includes a tiny clump of dark red flowers, sometimes rising slightly above the lacy mass of white flowers. Charles Darwin concluded this ‘spot’ was unlikely to have any real purpose but many flowers and groups of flowers have spots and it’s thought these days** they attract pollinators.

They do this either by creating an attractive colour or texture, guiding navigation or mimicking the pollinator (giving the impression of a safe, welcoming flower, or perhaps an insect to mate with!). I wrote a little about the latest research on flower spots on my blog a few months back.

Image: A Wild Carrot on the roadside near Malaga, in southern Spain, with a small clump of dark red-black flowers sticking out of the flat, white flowering structure.

*This Passion for Plants posting will also appear on the ABC Sydney website (possibly under 'gardening'), and is the gist of my 702AM radio interview with Simon Marnie on Saturday morning, between 9-10 am.

**'These days' being 2010. In the summer 2013 issue of Kew Magazine (the member magazine of Royal Botanic Gardens, Kew) there is a short item headed 'Tall, dark and mysterious', summarising a new interpretation of these small dark lumps. It seems that rather than attracting insects they might repel them, or at least insects the plant doesn't want such as gall midges. The gall midge lays its eggs in the developing fruits of the Wild Carrot. In a paper published in 2013 by Sabrina Polte and Klaus Reinhold, in Plant Species Biology, it's suggested that this warty central flower may 'mimic an already developed gall...[deterring] other midges from laying their eggs'. Polte and Reinhold filmed 883 insects landing on the flowers and examined flower heads for presence of galls - 50% of flower heads without the lump were afflicted while only 38% with it, and the former had three times as many galls. 

2 comments:

oliviakaylee said...

Thanks for your info. I really enjoy this post.

green planet

Tim Entwisle said...

In the summer 2013 issue of Kew Magazine (the member magazine of Royal Botanic Gardens, Kew) there is a short item headed 'Tall, dark and mysterious', summarising a new interpretation of these small dark lumps. It seems that rather than attracting insects they might repel them, or at least insects the plant doesn't want such as gall midges. The gall midge lays its eggs in the developing fruits of the Wild Carrot. In a paper published in 2013 by Sabrina Polte and Klaus Reinhold, in Plant Species Biology, it's suggested that this warty central flower may 'mimic an already developed gall...[deterring] other midges from laying their eggs'. Polte and Reinhold filmed 883 insects landing on the flowers and examined flower heads for presence of galls - 50% of flower heads without the lump were afflicted while only 38% with it, and the former had three times as many galls. Tim