The Aussie bush that hopped

By Tim Low 3 February 2016
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The world was taken over by an Australian plant long before our eucalypts and wattles were grown abroad, says Tim Low.

STICKY HOP-BUSH (Dodonaea viscosa) is a shrub I have come across in more places than I can mention, including the side of a volcano in Hawaii, coastal dunes in India, granite hills in South Africa, white sands in the Cocos-Keeling Islands and pine woodlands in Florida.

Other places to which it is native include the foothills of the Himalayas (up to 4000m high), the valleys of Peru, the mountains of Yemen and Ethiopia, the coast of Nigeria, scrubs in Borneo and Fiji, and the Chatham Islands far south of New Zealand. In Australia it grows in every state, from the tropics to southern Tasmania.

The two most extreme places I’ve seen it are in the New Guinea highlands and the Simpson Desert.

How can one species be versatile enough to master giant mountains soaked in rain and a hot desert? Unfortunately, I can’t offer an answer for this – no one knows.

Dodonaea viscosa photographed in Hawaii. (Image: David Eickhoff / Wikimedia)

Australia has almost 70 species of hop-bush (Dodonaea), named for their role in place of real hops for brewing beer. The bitter-tasting capsules were heavily harvested in the 19th century, producing a beverage said to be of ‘excellent quality’.

Only one of the many hop-bushes has gone global, and this adds to its mystique. Its travels started less than two million years ago, according to a recent DNA study. The sticky hop-bushes in Africa, Asia, and the Americas can be traced back to seeds that departed from Queensland, while those in New Zealand came from somewhere else in Australia. The seeds float for up to 60 days in salt water.

One advantage it has is that sticky hop-bush can assume many forms. It can grow as a small tree up to six metres tall or sprawl flat on the ground. Leaf shape and size vary so much that botanists once thought many species were involved. Even on one plant leaves can vary greatly. When squeezed, they feel slightly sticky. The stickiness may protect them from the jaws of some insect enemies, though it is not especially effective.

This Australian plant should be famous but suffers an image problem. It’s not photogenic, with leaves that often look ragged from damage by insects. It doesn’t have a memorable name. The other drawback is that we can’t yet explain its success. Saying it adopts many forms is something, but why can’t all plants do that?  

Tim Low is the author of the award-winning book Where Song Began. Follow him on Twitter @TimLow5.