What it is
Hura crepitans, the sandbox tree, dynamite tree, or monkey no-climb — a large, fast-growing tree of the tropical Americas, and one of the most dramatic and dangerous of all trees.
It belongs to the spurge family, Euphorbiaceae — the same family as the rubber tree, tung and candlenut, and jatropha — and, like many of them, it is armed with a caustic, toxic latex. It is a formidable tree in every way: its trunk is densely covered in sharp, conical spines (hence "monkey no-climb"), its sap is dangerously poisonous, and its fruit is, quite literally, explosive.
The exploding fruit
The sandbox tree earns its "dynamite tree" name honestly. Its fruit is a woody, pumpkin-shaped capsule of a dozen or more segments, and when it dries and ripens, it explodes — bursting apart with a loud bang audible from a distance, and flinging its flat seeds outward with astonishing violence.
The seeds are launched at speeds measured at up to 70 metres per second (around 250 km/h), and can travel 40 metres or more from the tree — one of the fastest and most powerful of all plant movements, a ballistic seed dispersal taken to an extreme (the gentler versions of the same trick are seen in gorse, witch hazel, and many other pod-bearers). The exploding pods are enough of a hazard that people are warned not to stand under a fruiting sandbox tree, and the empty, segmented pods were historically used — before blotting paper — as little containers of fine sand for blotting ink, which gave the tree its "sandbox" name.
Poison and defence
The sandbox tree is armoured at every level. Beyond the spiny trunk and the exploding fruit, its milky latex is caustic and poisonous — it burns and blisters the skin and eyes and is toxic if swallowed — and the seeds are violently purgative and poisonous.
This chemistry was put to use by Indigenous peoples of tropical America: the toxic sap was smeared on arrow and dart tips as a poison, and poured into pools to stun fish for easy harvest (the same fish-stunning trick used with the desert date, monkey orange, and buckeye). The tree's formidable defences — spines, poison, and exploding fruit together — make it one of the best-protected of all trees, and a striking example of how thoroughly a plant can arm itself. See historical ecology. Despite all this it is sometimes planted as a large shade and avenue tree in the tropics — carefully, and away from where its fruit can fire on passers-by.
Growing it
Tropical, frost-tender, and a tree of the hot, humid lowland tropics, the sandbox tree wants heat, high rainfall, and deep, moist, well-drained soil; it is fast-growing, large, and spreading, tolerant of a range of conditions but intolerant of cold and drought.
It is grown from seed (handled with care, given the toxicity) and as a fast shade and timber tree (its light wood is used for boxes and plywood), but always with respect for its spines, its poisonous sap, and — above all — its exploding fruit, which make it a tree to admire from a safe distance. It is included here as one of the most remarkable of all trees in its defences and its dispersal, rather than as one to plant casually. See propagation.
See also
- Rubber, Tung and Candlenut, and Jatropha its spurge-family relatives
- Gorse and Broom and Witch Hazel other trees with ballistic, exploding seed dispersal
- Desert Date, Monkey Orange, and American Buckeyes other fish-stunning poison plants
- Historical Ecology the sandbox tree's sap as arrow poison
- Tropical Fruit Trees the wider tropical-tree context
- Coral Tree another spiny tropical tree