Jul 14, 2018
Now that the rainy season seems to be over here at least, I'm finally introducing a plant I often see this time of year. I'm not sure if it grows all over Japan, but it seems to be native to Asia in general. The name tsuyukusa literally means "rainy season grass" but I've seen it translated as "dew herb" and "Asiatic dayflower" also.
When I first saw the plant I thought it looked familiar, but it wasn't rau ram (also known as Vietnamese coriander) like I thought. It didn't have any strong smell. I read that the plant is used as a medicine and food in China and India, but I've never seen anyone growing it as a food in Japan.
The most characteristic thing about the plant is its unique flowers. They are blooming from the rainy season into the summer, but each flower will only stay open for one day. The small flowers are a blue violet and have only two petals, but if you look carefully, there is one smaller white petal at the bottom. The blue petals used to be collected to use for pigment-making for woodblock printing. I've seen preschool students paint with ink made from akajiso, or red shiso, and asagao, or morning glory. It seems like it would be a similar process.
Tsuyukusa grows like a weed around here – in vacant lots or on the side of the road. I first saw it growing thickly inside of the runoff and irrigation canals leading to the river. It's a plant I associate with the rainy season and summer in Japan, much like dokudami (known as heart leaf and so many other names), which also grows like a weed everywhere. They are both plants you'll see featured in summertime illustrations, along with hydrangeas of course.
Have you seen tsuyukusa growing in your neighborhood?