Hura crepitans, the sandbox tree, also known as possumwood, monkey no-climb, assacu (from Tupi asaku) and jabillo, is an evergreen tree in the family Euphorbiaceae, native to tropical regions of North and South America including the Amazon rainforest. It is also present in parts of Tanzania, where it is considered an invasive species. Because its fruits explode when ripe, it has also received the colloquial nickname the dynamite tree.

Description

The sandbox tree can grow to 60 m in height, and up to 44 ft in girth at 6 ft above the ground; its large ovate leaves grow to 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 long, 5 - 8 cm diameter, with 16 carpels arranged radially. Its seeds are flattened and about 2 cm diameter. The capsules explode when ripe, splitting into segments and launching seeds at 70 m/s. One source states that ripe capsules catapult their seeds as far as 100 m. Another source states that seeds are thrown as far as 45 m from a tree, with a mode of about 30 m. High-speed video analysis of its exploding fruit revealed that Hura crepitans seeds fly with backspin as opposed to topspin, which was previously assumed. Backspin helps seeds remain oriented to minimize their drag during flight.

Habitat

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.

Uses

Its wood is light enough that indigenous people used it to make canoes. Fishermen have been said to use the milky, caustic sap from this tree to poison fish. The Caribs made arrow poison from its sap. 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. 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.

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