For most of the year you could walk right past a Cercidiphyllum japonicum tree without a second glance but in autumn it always stops people in their tracks - not just because of its autumn colour but because of its wonderful aroma. As the leaves turn yellow they produce a compund called maltol, which makes the whole tree smell of burnt toffee, rather like a toffee apple or candyfloss stall. Maltol is used as a flavour enhancer in the food industry, where it's known by the E number E636.
This specimen is in Durham University Botanic Garden but about five years ago I planted one in my own garden - and it has grown remarkably quickly. It's rather a large tree for a small garden - reaching 45m. in the wild, but it will be a while before mine becomes a problem. Katsuras, which are native to China and Japan, are supposedly frost-sensitive but mine came through last winter's prolonged snow and ice without any sign of damage. It will be interesting to see how the tree copes with a hot, dry summer (if we ever get another one here), as under those conditions it sheds all its leaves as a drought-avoidance mechanism, then refoliates when the rain returns - so can have two 'springs' in a single season.
This autumn year I collected a bag of those toffee-scented leaves to keep through the winter and sniff occasionally - as a reminder of that wonderful aroma on a warm, sunny afternoon.