Have you ever wondered why can't all leaves be the same type? Why are there so many different leaf types anyway?
One thing is for sure, they are not so for our amusement. It is, in fact, a mechanism used by nature to sustain life on Earth.
Leaves act like food factories for trees. They carry out the process of photosynthesis to supply the tree with carbohydrates. During photosynthesis, leaves absorb sunlight and carbon dioxide and give out oxygen into the environment. When pores on the leaves (called stomata) open to absorb carbon dioxide from air, water evaporates from the pores by transpiration. If leaves absorb excessive heat from sunlight during photosynthesis or lose excessive water during transpiration then they can burn out or get dehydrated. Hence, a balance is needed between photosynthesis and transpiration for trees to survive.
Through evolution, the overall design and structure of leaves have adapted to suit the climate (including temperature and rainfall) and nutrient availability around them.
Shape:
The number of possible leaf shapes is probably innumerable. Here, we have compared the properties of two very different shapes to understand how resourceful nature can be: broad, open leaves and thin, needle-like leaves.
Size:
Another adaptation leaves uses for survival is their size. Sunlight, rainfall, and temperature during day as well as night time play important role in deciding leaf size.
In hot and dry climate, small leaf size helps to reduce overheating (example: deserts).
In hot and wet climate, leaves receive enough sunlight as well as moisture. They can, thus, afford to grow large (example: rainforests).
In cold climate, leaves are small to protect themselves from frost (example: mountains).
Margin:
In addition to shape and size, margin of leaves can also be of several types and determine the efficiency of photosynthesis.
Serrate margin provides additional surface area for photosynthesis. This is specially useful to start early photosynthesis in colder regions with short growing season.
Trees in warmer climate tend to have smoother margins as they are already capable of efficient photosynthesis and do not require additional surface exposure.
Just like you and me, leaves are highly sensitive to their environment. When the same tree type is grown in different climates, the leaves develop differently according to the conditions around the tree.
So the next time you go out, have a look at the leaves around you. Does their shape tell you anything about your surroundings?
Sources and further reading:
Cover image: Leaves Spreaded by Alex Latimer, for Toast written by Helen Moffett, published by Book Dash (©Book Dash, 2018) under a CC BY 4.0 license on StoryWeaver. Read, create and translate stories for free on www.storyweaver.org.in
Leaf Shapes and Arrangements (http://theseedsite.co.uk/leafshapes.html)
Deciduous Or Evergreen The Adaptive Choices That Plants Make. (https://www.climate-policy-watcher.org/tropical-rainforest/deciduous-or-evergreen-the-adaptive-choicks-that-plants-make.html)
Comparing Conifers and Deciduous Trees. (https://www.wnps.org/blog/conifers-deciduous-trees)
New research unlocks the mystery of leaf size (https://theconversation.com/new-research-unlocks-the-mystery-of-leaf-size-83294)
Nix, Steve. "Tree Leaf Margins: Toothed and Entire: Tree Leaf Key." ThoughtCo, Feb. 11, 2020 (https://www.thoughtco.com/tree-leaf-margins-toothed-leaf-key-1343489)
Leaf Edge (margin) (https://en.wikipedia.org/wiki/Leaf#Edge_(margin))
Daniel J. Peppe, Dana L. Royer, et al. Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications. New Phytologist, 190, 724-739 (2011). (https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.2010.03615.x)