Plant Life: Katsura Tree

Autumn in the Air

One of the heralds of fall is the large Katsura tree (Cercidiphyllum japonicum) in the Japanese Garden next to the main road running from the Gatehouse to the Residence at Bloedel Reserve. Normally Katsuras are among the first trees to begin losing their leaves each autumn, and ours begins shedding its foliage in August. But before you see any leaves dropping, you will notice a pleasant fragrance as you pass by.

As you look around, you won’t see any flowers in bloom because the scent is, in fact, coming from the Katsura leaves themselves as they begin to turn yellow and then brown. As more and more leaves change color, the scent becomes stronger. If you are at the Katsura and you don’t notice the sweet scent it gives off, wait for a minute or so. Even a gentle breeze can disperse the fragrance, but it will return if you linger long enough. When asked to describe it, people often compare the scent to cotton candy, burnt sugar, or even peaches.

Making Sense of Scents

The chemical molecule that is partly responsible for the distinctive fragrance is maltol. Maltol also contributes to the pleasing smells of baking bread, coffee and cocoa, to name just a few. Maltol is now commonly used commercially in flavor enhancers, perfumes, and incense. Interestingly, not everyone can detect it. For some people the scent of maltol is quite pronounced, while others don’t have the scent receptors to pick it up.

Although maltol is present even in new Katsura leaves, you can’t smell it in the spring. But when autumn nears and the leaves begin to turn yellow, they produce more maltol. During this color change, the additional maltol combines with sugars in the leaves, and that is when the scent becomes noticeable. The exact purpose of maltol in Katsura leaves is still unknown. But its distinctive fragrance is one of the sensory delights guests can experience in the Japanese Garden every fall.