Plant Talk | Science Talk

The Cannon Ball Tree

Scott A. Mori has been studying New World rain forests for The New York Botanical Garden for over 35 years. He has witnessed an unrelenting reduction in the extent of the tropical forests he studies and as a result is dedicated to teaching others about this species rich ecosystem.


A tangle of flowers arising from the trunk of a cannon ball tree in Grenada. (Photo by Scott A. Mori)

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I still stand in awe each time I see the cannon ball tree (Couroupita guianensis), a member of the Brazil nut family. In fact, it is such an astonishing plant that I am nominating it as the most interesting tree on Earth (disclaimer: I am a specialist in the Brazil nut family and my nomination may be biased). After you read this essay, I would like to know if you agree with me—if not, I challenge you to nominate a tree, tropical or temperate and from any part of the world, that you feel is more interesting than this marvel of nature.

In nominating your tree, consider the aroma of the flowers or fruits, interesting plant or animal interactions, economic use, ecological dominance, or any other criteria that you think merits recognition. Until the end of the Tropical Paradise show, I will continue to introduce you to tropical plants that have impressed me over the course of my career.

Cannon ball-like fruits of Couroupita guianensis, the cannon ball tree. Photo by L. Gamez Alvarez.

Cannon ball-like fruits of Couroupita guianensis, the cannon ball tree. (Photo by L. Gamez Alvarez)

Unfortunately, because the cannon ball tree can only grow outside of its natural habitat when cultivated in subtropical and tropical botanical gardens, it can not be found at the NYBG. However, if you have a chance to visit the Miami area, you can appreciate it in cultivation at the Fairchild Tropical Botanical Garden in Coral Gables. In the meantime, you can enjoy tropical plants throughout all seasons in the Enid A. Haupt Conservatory, including Gustavia augusta, another member of the Brazil nut family.

The cannon ball tree is planted in gardens because the flowers, arranged on long stalks projecting from the trunk, are large, beautiful, pleasantly aromatic, and unlike any other flower a newcomer to the tropics has ever seen. Even the fruits are a botanical curiosity because they mimic the shape and size of cannon balls, but, in contrast to the flowers, they release a fetid aroma at maturity when they hit the ground and break open.

Flowers of the cannon ball tree are without nectar, but bees are rewarded for visiting them with a special kind of pollen. The structure of the male part of the flower (the androecium) is found only in the Brazil nut family. Fertile stamens occur in a ring surrounding the style, but what makes the flower different is the unilateral prolongation from one side of the ring, bearing the staminodes with antherodes that contain pollen that never germinates (in contrast, the pollen of the ring is fertile and does germinate). The pleasant aroma attracts the pollinators to the flowers and the yellow color at the apex of the staminodes directs bees to the sterile pollen, especially female carpenter bees (Xylocopa brasilianorum), that gather the sterile pollen to feed their larvae. While they are collecting sterile pollen, fertile pollen is deposited on their heads and backs, where it is subsequently rubbed onto the stigmas of the next flowers visited, thereby effecting cross-pollination–the first step in the production of seeds.

Lateral view of a cannon ball tree flower showing the location of the fertile stamens and the staminodes. Photo by Scott A. Mori.

Lateral view of a cannon ball tree flower showing the location of the fertile stamens and the staminodes. (Photo by Scott A. Mori)

At maturity, the cannon ball-like fruits fall to the ground where they often crack open, revealing a mass of bluish-green pulp that exudes a fetid aroma and surrounds hundreds of seeds. Mammals (such as peccaries and pacas) further break open the fruits and swallow the pulp along with the seeds. Protected by specialized, intertwining hairs, the seeds pass through the mammal’s digestive track and germinate away from the mother tree, where they have a better chance of growing into the next generation of cannon ball trees.

For those interested, more details and images of this fascinating tree can be found on our scientific website dedicated to the Brazil nut family as it occurs in the Neotropics.

  1. My favorite tree is the native Hawaiian wiliwili, with its fabulous crab-claw blossoms that range from pearly green to scarlet. Its thorny trunk expands during the rainy season to hold all of the moisture it subsists on during the dry season, when it loses its leaves and goes dormant. The trunk has stretch marks to show where it has expanded in winter and shrunk in summer. This remarkable tree has four stages: flush with green heart-shaped leaves, decorated with flamboyant blossoms, ripe with spiral seedpods bursting open to reveal ruby red or yellow seeds, and completely barren: empty octopus-like arms reaching toward the sky without a leaf or flower to petition for them.

    Native Hawaiians made surfboards from the tree’s buoyant wood and leis from its flowers and seeds. They also noted that “when the wiliwili blooms, the sharks bite.” Late summer, when the flowers erupt on the dryland forest tree, the sharks are pupping near shore and more likely to aggressively chase away an unsuspecting swimmer.

    http://www.mauimagazine.net/Maui-Magazine/September-October-2011/Return-of-the-Wiliwili/

  2. Scott A. Mori says:

    Dear Sharon,

    The Hawaiin WilliWill tree is a legume (Erythrina sandwicensis) and is certainly a worthy nomination and you described it very well. However, I still think that the cannon ball tree is the most interesting tree on earth because of its interesting pollination and dispersal systems. Can you tell us if the williwilli tree has similar stories? Is so, I might reconsider.

    Scott

  3. Tom Andres says:

    Just don’t stand in awe underneath these majestic trees when the fruits are ripening! The common name is quite apt.

  4. Scott A. Mori says:

    Hi Tom,

    Don’t worry, I wear a motorcycle helmet when I am admiring them.

    Scott

  5. MuseumsNYC says:

    My favorite tree is the Sapodilla (Manilkara zapota) also known as the Chicle tree. It’s my favorite because it was through this tree that I was introduce to the wonders of nature as a child.

    When I was a kid, maybe 6 or 7, my granduncle would visit us maybe once or twice a month. I loved his visits not only because he would bring me candies and toys but also because he was a great storyteller. I particularly love his “chiclero” stories, back when he was in his 20s he worked in the jungles of Peten, Guatemala, harvesting the tree’s sap which was used to make gum. There were stories about climbing trees, using his machete to cut channels down the tree, collecting and boiling the sap, bringing the final product to market while trekking miles out of jungle. Then there were the great stories about the animals that lived on or used the tree, like howling monkeys, coatis, tapirs, toucans, fruit bats, snakes and even jaguars. Other stories were about the dangers of the jungle, like when he had malaria or when he was bitten by a botfly and had to use a burning cigar to force that larva out. Nasty stuff!

    Every week was a different story, great memories!
    I guess you can say the Sapodilla is part of our “family tree.”

    Oh, and the fruit taste good too, I think they used to called chico zapote.

  6. Scott A. Mori says:

    Hi MuseumNYC,

    The sapodilla is another fantastic plant and worthy of nomination. In addition to the things you mentioned, It is interesting because bats are important pollinators of this species and eat the fruits but, because of their large size, it does not seem that they would be efficient dispersal agents.

    I would have loved to hear the stories told by your uncle.

    Scott

  7. MuseumsNYC says:

    Thanks Scott, had a great time remembering them.

    Check this amazing picture of a bat eating a sapodilla fruit!
    http://bit.ly/Vr3kzP

  8. Scott A. Mori says:

    Thanks for sending this link to the picture. I checked the following book:

    Lobova, T. A., C. K. Geiselman & S. A. Mori. 2009. Seed Dispersal by Bats in the Neotropics. Memoirs of The New York Botanical Garden 101: 1-471

    There are many records of bats visiting, eating, and probably even dispersing the seeds of this plant. Generally speaking bats enjoy the same fruits as we humans enjoy.

    Scott

  9. Mary Collins says:

    Hi Scott, Over the past year or so, our Director, Carl Lewis, has been pollinating our Couroupita. We have some seedlings in 1-gallon size containers. Would you like one for the conservatory at NYBG? Dennis Stevenson often visits Fairchild and perhaps I can get him to bring a plant back with him.

    Best wishes,
    Mary Collins
    Senior Horticulturist

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