Fruit: we humans think it’s the very definition of nature’s bounty, and ever since that first forbidden apple fruit has been considered luscious and desirable. But fruit isn’t here to please or tempt us, instead we animals are here to serve it. Wolfgang Stuppy and Rob Kesseler’s book Fruit: Edible, Inedible, Incredible reveals the host of clever tricks fruiting plants have developed to spread their seeds, including enticements, disguise, and aerodynamic engineering.
The book also revels in the “bewildering diversity” of fruit through photos stitched together from scanning electron microscope images.
This flower bud of the winter’s bark tree, native to Central and South America, gracefully displays all the elements of the fruit process ahead of it. The orange structures, called carpels, will swell into fruit when the flower is pollinated. The longitudinally sliced carpel in the middle reveals the ovules inside, which will develop into seeds. Towards the edge of the flower bud the pollen sacs are visible, with tiny pollen grains inside.
The carpel protects the ovules, as the fruit later protects the seed. Wolfgang Stuppy writes that this gives fruiting plants tremendous evolutionary advantages over “naked seed” plants, or gymnosperms, like conifers and Ginkgos.
Hitching a Ride
Once a fruit has grown to maturity, the next step is to find a way to head off into the world, where its seeds may take root in distant landscapes, strengthening the species by allowing for the exchange of genes between different populations.
Many low-growing plants have adopted a simple dispersal strategy: develop fruit with burs or spikes that snag the fur of passing animals. The Pima rhatany is a shrub native to Mexico and the southern United States. Its diminutive fruits (about one-third of an inch wide) are covered in barbs.
Catch the Wind
Another dispersal strategy is to wait for a fair breeze, and then to ride it as far as possible. Sometimes the entire fruit becomes airborne; other times the fruit cracks open to let its seeds fly away.
In this picture the seed, from the American bugbane plant, is adapted for air dispersal with dozens of protrusions to help it float buoyantly on the wind. Other aerodynamically inclined fruits use structures resembling parachutes, shuttlecocks, and Frisbees.
A Peachy Keen Strategy
This close-up shows the downy texture of the peach. Researchers think the fuzz helps protect the peach from insects and disease.
The peach spreads its single seed by virtue of fleshy deliciousness: A number of mammals happily devour the fruit, and the seed’s large, armored shell allows it to pass safely through a large herbivore. And after it passes through the digestive tract, it conveniently emerges in a pile of fertilizer.
Some species in the citrus family are more technically known as hesperidia, a name derived from a Greek myth about a glorious garden in the west called Hesperides where “golden apples” grew. Scholars believe the Greeks were referring to sweet oranges.
Citrus fruits have been valued by many cultures throughout the millennia that they’ve been in cultivation. This oddity, called the Buddha’s hand, is considered a “freak” variety of citrus that emerged sometime after A.D. 300. Buddhist monks saw the praying hands of Buddha in its strangely graceful shape, and cherished the fruit as a symbol of happiness, wealth and longevity.
While the peel of the Buddha’s hand is aromatic and tasty in candy, it has very little flesh and is rarely eaten.
Now You See Me
While many berries sport bright, flashy colors to attract the attention of birds, blueberries seem dark and difficult to detect from afar. But that’s just when you look with human eyes.
This microscopic photo of a blueberry’s skin shows that the berry is covered in a powdery layer of wax platelets, which are highly reflective of ultraviolet light. Since birds can see ultraviolet wavelengths that humans can’t, a bird’s-eye view may reveal a spectacularly red berry.
A Devious Trick
In the Australian rainforest grows the monkey’s earrings tree, so called because of its decorative dangle of seeds. The tree’s fruits open up to reveal bright orange interiors that set off glossy black seeds, a contrasting color scheme that birds take as a clear signal that the tree has prepared a tasty meal for them. But looks can be deceiving.
The fruits of the tree have no fleshy, nutritious sections for the birds to derive energy from. Instead, the tree may have developed this color scheme to trick birds into consuming its seeds. While the concept of “fruit mimicry” remains controversial, botanists have observed some young, inexperienced birds consuming the worthless fruit.
Pity the poor Osage orange tree. Researchers believe this tree relied on just a few species to eat its fruit and disperse its seeds, but those animals went extinct thousands of years ago. Now when the tree drops its fruit in the fall, the brain-like orbs are left to rot on the ground.
The knobby Osage orange, about the size of a grapefruit, has the consistency of a raw potato and is mildly poisonous to today’s mammals. However, researchers think it may have been a very palatable treat for extinct mammals like mammoths, mastodons, or the giant ground sloths that tromped across North America until around 13,000 years ago.
All Images©Rob Kessler