From the big, flat paddles of the South American monstera to the tiny, round bobbles of the African string-of-beads plant, leaves come in a bewildering variety of shapes and sizes. Their main job is to harvest sunlight and then use this energy to help the plant make food via photosynthesis. Carbon dioxide and water are converted to glucose and oxygen inside specialised structures called chloroplasts.
Leaf structure has a big impact on this process. Leaves with bigger surface areas, for example, can pack in more chloroplasts and absorb more sunlight, which means they can make more glucose. It sounds like a good thing, only those same large leaves may be more prone to heat loss, which is a problem if the plant lives somewhere chilly.
There’s a trade-off to be had; nutrients versus heat loss, and over time, leaf shape evolves towards the optimal solution. The problem, however, is that plants are bombarded with a constant maelstrom of trade-offs, including the ability to transport water efficiently, minimise water loss, repel pathogens and deter hungry herbivores. Different species of plants living in the same ecosystem sometimes evolve different leaf shapes because often, there’s more than one solution to the trade-offs that they face.
Hornbeams and beech trees, for example, live in the same deciduous woodlands and have evolved similarly shaped leaves, fringed with tiny serrations. Meanwhile, oak trees, which live in the same ecosystem, have evolved lobed leaves with smooth edges. Subject to almost identical environmental conditions, and the same array of trade-offs, the hornbeam and the beech have arrived at one answer to the problem of leaf design, while the oak tree has adopted a different, but equally excellent solution.
Read more:
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- Why are seeds such different sizes?
- Why do some trees have smooth bark and others rough?
- How have plants evolved to mimic insects when they don’t have vision?
Asked by: Belle Ford, Southport
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