Leaves have to do a lot more than just gather sunlight for photosynthesis. They also transport nutrients, take in carbon dioxide and oxygen, deter animals from eating them, and release water to cool the plant by evaporation, all while being sturdy enough to resist the physical battering of the wind and rain. That’s a lot of different overlapping problems to solve at once, and every plant has a different set of priorities, according to the demands of its environment.
Nevertheless, it’s still remarkable how much the leaves of the flowering plants and trees vary, when compared to the much more conservative designs of the conifers and ferns. Pelargoniums, which are popular houseplants, all belong to the same genus, but the different species have a huge variety of leaf shapes, from wispy fronds to broad heart shapes.
Exactly how this happens is still a hot topic of research, but it seems that flowering plants have a few important structural genes that can cause dramatic changes to the leaf shape, with just minor genetic mutations.
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