Hura crepitans

The sandbox tree can grow to 60 metres (200 ft) in height,^[7] and up to 13 metres (44 ft) in girth at 1.8 metres (6 ft) above the ground;^[8] its large ovate leaves grow to 60 cm (2 ft) wide. The trees are monoecious, with red, un-petaled flowers. Male flowers grow on long spikes, while female flowers grow alone in leaf axils. The trunk is covered in long, sharp spikes that secrete poisonous sap. The sandbox tree's fruits are large, pumpkin-shaped capsules, 3–5 cm (1–2 in) long, 5–8 cm (2–3 in) diameter, with 16 carpels arranged radially. Its seeds are flattened and about 2 cm (3⁄4 in) diameter. The capsules explode when ripe, splitting into segments and launching seeds at 70 m/s (250 km/h; 160 mph).^[5] One source states that ripe capsules catapult their seeds as far as 100 m (330 ft).^{[9][verification needed]} Another source states that seeds are thrown as far as 45 m (150 ft) from a tree, with a mode of about 30 m (100 ft).^[10] High-speed video analysis of its exploding fruit revealed that Hura crepitans seeds fly with backspin^[11] as opposed to topspin, which was previously assumed.^[7] Backspin helps seeds remain oriented to minimize their drag during flight.^[12]

This tree prefers wet soil, and partial shade or partial to full sun. It is often cultivated for shade. Sandbox trees are tropical trees and prefer warmer, more humid environments.

Its wood is light enough that indigenous people used it to make canoes.^[13] Fishermen have been said to use the milky, caustic sap from this tree to poison fish.^[14] The Caribs made arrow poison from its sap.^[15] The wood is used for furniture under the name "hura". In a time when most writing pens left wet ink on the page, the trees' unripe seed capsules were sawn in half to make decorative boxes (also called pounce pots) to hold the "sand" used to dry it, hence the name 'sandbox tree'. It has been documented as a herbal remedy.^[16]

The seeds contain an oil that is toxic for consumption but can be made into biodiesel and soap; the starchy leftovers after extracting the oil from the seeds can be made into animal feed after cooking.^[13]

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  Large sandbox tree in Honolulu
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  Hura crepitans in Vietnam
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  Hura crepitans in Saint John, U.S. Virgin Islands
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  Spiny trunk of Hura crepitans
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  Leaf of Hura crepitans
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  Hura crepitans fruit carpel
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  Hura crepitans fruit carpel, opposite side

 

Wikimedia Commons has media related to Hura crepitans.

• Center for Wood Anatomy Research, details about the wood of the Sandbox tree
• (in Portuguese) University of São Paulo: Hura crepitans photos
• www.maya-ethnobotany.org seedpod explosion video