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Faced with the problem of dispersing seeds, flowering plants developed special seed-carrying structures that are perhaps most familiar to you from your visits to the grocery store. This episode, we discuss the evolution, functions, and incredible diversity of Fruit.
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Fantastic Fruits
A fruit is a thing made by angiosperms (flowering plants). Specifically, it is a seed-bearing structure formed from the ovaries of flowers. All flowering plants form fruits, and flowering plants are extraordinarily diverse, so it’s no surprise that fruits come in many, many varied forms.
Top left: A chestnut fruit and beech fruit. Image by Aly Baumgartner (thanks, Aly!)
Top right: A brazil nut. Image by Lior Golgher, CC BY-SA 4.0
Bottom left: A wallflower silique with seeds. Image by Stefan Lefnaer, CC BY-SA 4.0
Bottom right: A dandelion clock. Image by Richard Bartz, CC BY-SA 2.5
Fruits can differ in many respects, including: their size and shape; the number of seeds contained within (from one to many); the extent of tissue surrounding the seeds; and which flower tissues are actually involved in fruit formation. Many of the terms we use to describe fruits – such as “berry” or “nut” – mean different things when used by biologists versus at the grocery store (bananas are botanically considered berries, for example!).
Image by Alvesgaspar, CC BY-SA 3.0
Despite their very varied forms, fruits tend to share a function: to help seeds get where they need to go. In some fruits, it’s as simple as dropping off the tree when they’re ripe; in others, the fruits have shapes that catch the wind (such as maples and dandelions), allowing their seeds to fly off to somewhere new. Many fruits naturally split open to release the seeds inside. And some fruits literally explode to send seeds flying off into the distance.
Probably the most famous seed-dispersal strategy of fruits is to get animals to do the job. Many plants have evolved fruits that are delicious, encouraging herbivores to eat them, after which point the seeds will eventually be deposited somewhere else, along with a fresh pile of fertilizer. It’s no surprise that we humans have domesticated so many fruit-bearing species.
Fruity Fossils
The fossil record of fruits extends back into the Cretaceous Period, when angiosperms were on the rise. Fruits are often preserved as compression fossils (like leaves), though they are occasionally mineralized in three dimensions. As is usually the case with plants, fruit evolution is closely related to the evolution of herbivorous mammals, including a peak in diversity during the Eocene, around the same time many modern groups of mammals were getting their start.
Top left: Fossil sycamore fruit from Paleocene Alberta. Image by Georgialh, CC BY-SA 4.0
Top right: Fossil beech fruit from Eocene Washington. Image by Kevmin, CC BY-SA 4.0
Bottom left: Fossil maple-like fruit from Eocene Washington. Image by Kevmin, CC BY-SA 4.0
Bottom right: Fossil Physalis fruit from Eocene Argentina. Image by Peter Wilf, CC BY 4.0
Fruit and seed fossils are often key to our ability to understand plant evolution (especially how they dispersed their seeds) as well as ancient food webs. Some of the most exciting fruit and seed fossils have been found in the guts or poop of ancient herbivores!
Learn More
The Science of Plants: Fruit Morphology
Digital Atlas of Ancient Life: Fruits
Digital Atlas of Ancient Life: Fruit and seed dispersal
The earliest known fruit-eating birds, Jeholornis from the Early Cretaceous
Co-evolution of angiosperms and fruit-eating animals (technical, open access)
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