A. polystachya

Fruits of A. polystachya through binoculars

Leaves of A. polystachya through binoculars 

Just as the fruiting season begins, we are thrilled to announce the discovery in Hong Kong of Aphanamixis polystachya, a grand lowland tree that can grow up to 30 meters, bears pendulous bunches of colourful capsules in the autumn and winter months. Aphanamixis polystachya occurs naturally throughout tropical Asia, being present in Southern China, India, Sri Lanka, Thailand, Vietnam, Laos, Vietnam, Malaysia, Indonesia, the Philippines, New Guinea and the Solomon Islands. Whilst of great interest to ecologists in Hong Kong, its discovery here is therefore not too surprising. The species is normally found in broadleaved evergreen forest at low to middle elevations.

Much of Hong Kong’s biodiversity has been heavily affected by land use change for millennia, but plant species that grow in the lowlands have had it worst. This is because the natural vegetation of coastal areas, flood plains and valley bottoms were settled by humans first, and lower hill slopes were converted to farmland thereafter. Very few natural lowland plant communities remain as a result and rapid urbanisation over the past century has meant that many lowland species have lost out to roads and buildings. Such degradation has pushed many species to extinction and reduced the occurrence of many others to tiny pockets of old growth remnants, such as fung shui woodland.

The fruits of A. polystachya appear in big clusters that dangle the length of a forearm. When fresh, individual fruits are spherical and spongy, with an apple green coat. But as they dry and turn orange, the coat splits open to reveal fiery red aril wrapped seed inside. The size and texture of the fruits suggests that they offer a high energy meal that is able to sustain large birds. It has been shown that woodpeckers are specialised in feeding on the seeds of related species in the Meliaceae, the large, tropical plant family to which Aphanamixis belongs.

Some of you might ask, how is it possible that this newly discovered tree, with such showy fruits, has remained hidden, out of the gaze of sharp-eyed botanists, until now? Our scientists suppose that this year could be a mast fruiting year for A. polystachya in Hong Kong. Mast fruiting is a feature of many dominant forest trees that fail to fruit every year but which do so synchronously and in very large quantities when they do. This would make it possible to spot their crop before it gets devoured by frugivores. With its large, glossy compound leaves, A. polystachya looks surprisingly similar to several other species of the Meliaceae. On top of habitat destruction, the species has also suffered due to intensive exploitation for timber and boat building in the past.

Discoveries such as these remind us of the incredible biodiversity of Hong Kong. We are looking forward to more exciting finds in the coming months!