Katsura tree
Nothing signifies the onset of autumn more to me than the smell of candy floss or caramel wafting across a sun-bathed garden from the Katsura tree. One of the very first trees into leaf in a garden setting in the United Kingdom, this is also just about the earliest to display its autumn finery and as it does so, to emit this wondrous fragrance. Throughout the year this tree stores complex sugars in its leaves and then at the onset of leaf drop these complex sugars break down into their constituent parts for reabsorption by the plant. A side product of this breakdown is the release of a small molecule called maltol and it is this molecule that is largely responsible for the beguiling aroma.
Once bare of leaves, one can see the characteristic opposite, clawed, red buds on the twigs. The emergence of the dainty, heart shaped leaves, initially tinged red, signals the first signs of spring. Continued close inspection as the season progresses will reveal the tree to have small and inconspicuous flowers that are either functionally male or female, but not both. Technically this is therefore known as dioecious (having 'two households'). This tree is one of two species in the genus with only this single genus in the family. Its nearest botanical relative is the witch hazel family (Hamamelidaceae).
Although it makes a fantastic addition to any garden, care must be taken with its siting as it is definitely a species that is susceptible to drought and prefers to be grown in moist soil. When suffering drought stress the tree will prematurely shed its leaves (and emit that characteristic aroma) and re-flush when sufficient moisture is again available. If this happens late in the season the new growth has insufficient time to harden off before winter and is then susceptible to damage by frosts.
In Japan, China and Korea this species is embedded in the folklore and celebrated in poetry where Katsura has been translated as the "moon laurel". Legend has it that a shadow on the moon is the result of a magic Katsura tree which cannot be cut down.
There is a magnificent, mature specimen growing near the centre of the Walled Garden as well as some younger specimens along the Acer Glade at the Arboretum. New plantings will continue to be made from seed collected in Hokkaido from the recent OBGHA Japanese expeditions.
Further reading
Tiefel P and Berger RG (1993) Seasonal variation of the concentrations of maltol and maltol glucoside in leaves of Cercidiphyllum japonicum. Journal of the Science of Food and Agriculture 63: 59-61.
Alison Foster