12 July 2013

Close Look At An Onion Flower

spathe of onion flower

The onions on Allotment90 are just about to flower.

If you innocently Google 'onion flower' you'll discover a torrent of onion flower anxiety. Once the flowers appear all is lost - your onions won't be winning any prizes in your local vegetable growing competition.

These may be the cries of alarm from experienced allotmenteers, and we may indeed rue the day the onions flowered, but for the moment I'm enjoying them. The stage they are at the moment - bursting with youthful ardour - brings an extravagant exoticism to the allotment.

And of course, they foster the need to learn new words ...

The thin, papery case courageously holding back the onrush of little flowers in the picture above is called a spathe, which is a form of bract.

perianth in onion flower

The individual flowers themselves (because we have already noted an onion flower is really an inflorescence of many flowers) haven't quite opened yet, so the perianth is still neat and virginal.

'The perianth?' I hear you cry. This is the calyx and corolla together.

'Oh no!,' I hear you cry, 'when will she stop with the words?' Not just yet, I reply.

I have a diagram up my sleeve ..

And now it all makes sense.

The Calyx
The calyx is the outermost whorl of a flower. It consists of sepals, that are green.

  • The calyx encloses and protects the inner whorls in the bud stage.
  • Since the sepals contain chlorophyll, they can also synthesize food

The Corolla.
The corolla is found on the inside of the calyx and is the most conspicuous part in the flower because it is usually white/brightly coloured . This whorl is made up of petals which are much larger than sepals.  The calyx and corolla together are called the perianth .

  • The brightly-coloured corolla attracts agents of pollination such as insects and birds.
  • The corolla encloses and protects the stamens and pistil.