• Question from:Adrian

What determines the shapes and sizes of leaves? Do darker leaves mean a higher chlorophyll content, if not, what determines the colour?

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  • At home in Ruardean, Gloucestershire, England
  • Posts: 625

Sorry that we've not been able to answer this.  Nearly six months on, I am afraid we have to write this one off.  I guess we have more zoologists on board than botanists!

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  • Horniman Museum, London, UK
  • Posts: 964

Hi Adrian, I'll have a go, although I can only offer suggestions.

Leaf shape is determined by a variety of factors - the amount of sunlight, the amount of water available, the amount of rain, the amount of snow, the amount of wind, etc. Plants in tropical rain forests often have large leaves with drip tips for collecting lots of light in the undercanopy and shedding rain, whilst pine needles are small and compact to reduce waterloss and damage caused by cold and wind.

Leaves have different pigments than just chlorophyll and their colour is determined by the amount of each pigment and the physical structure of the leaf (for example, thinner leaves will be a lighter colour because light can shine through them). The different pigments are each better at absorbing light of different wavelengths, so plants in the shade will need different amounts of certain pigments to get as much energy as possible from the different wavelengths of light to those that plants in the light would receive (if that makes any sense!).