Yutaka Suzuki, Photographer / Cultural Observer
International Symposium on Ethnobotany and Ecological Perception
Opening
Good afternoon, ladies and gentlemen.
It is a pleasure to be here today to speak about two remarkable plants—Reynoutria japonica and Reynoutria sachalinensis,
known in Japan respectively as Itadori and Oo-itadori.
What connects these two species is not only their shared genetics,
but also the curious gap between how they are perceived in Japan and how they are treated abroad.
1. Botanical Overview
Both Itadori and Oo-itadori belong to the Polygonaceae family and share a rhizomatous, bamboo-like morphology.
However, they differ significantly in size, leaf structure, and cytology
- Reynoutria japonica, or Japanese knotweed, is typically 1 to 2 meters tall,
with hollow stems and heart-shaped leaves about 10–15 centimeters long.
It is diploid, possessing 2n = 88 chromosomes. - Reynoutria sachalinensis, the Giant or Sakhalin knotweed, can reach heights of 3 to 4 meters,
with broad, cordate leaves up to 40 centimeters in length and 2n = 132 chromosomes.
It thrives in colder regions such as Hokkaido, Sakhalin, and the Russian Far East,
exhibiting deeper root systems and greater frost tolerance.
These differences illustrate an evolutionary divergence within the same genus,
one adapted to temperate climates, the other to subarctic environments.tany
2. The British Knotweed Crisis
As you know, R. japonica was introduced to Europe in the mid-19th century as an ornamental species.
Its beauty—those pale green stems and white clusters of flowers—soon gave way to fear,
as it escaped gardens and began colonizing riverbanks, railway embankments, and construction sites.
By the late 20th century, it was listed among Britain’s most damaging invasive plants,
its rhizomes capable of breaking through concrete and undermining entire buildings.
Around 2010, British authorities attempted biological control by introducing a small Japanese psyllid,
Aphalara itadori, an insect that feeds exclusively on the plant.
When I read this news, I wrote on Twitter—half seriously—that
“if you are going to let insects eat it, perhaps humans should eat it instead.”
The post unexpectedly went viral, and even the BBC covered it.
It seems the idea that a “weed” could be food was both amusing and revealing.
3. Cultural Contrast
In Japan, Itadori has long been foraged and eaten as a spring vegetable—boiled, pickled, or made into tempura.
The young shoots contain oxalic acid, giving them a refreshing tartness.
The plant’s name itself, Itadori, literally means “pain remover,”
and its roots have been used in traditional medicine for centuries.
Chemically, both R. japonica and R. sachalinensis are rich in resveratrol and related polyphenols,
which modern science recognizes for their anti-inflammatory and antioxidant properties.
Ironically, in the same decade that the United Kingdom sought to eradicate Japanese knotweed,
Japanese scientists and nutritionists were extracting the same species to create health supplements.
In my own case, I have been taking a supplement made from R. sachalinensis daily for joint support—
especially for my knees, which, after many years behind a camera, now appreciate its quiet benefits.
4. Reflections
This contrast—between eradication and appreciation, between pest and medicine—
reveals how cultural perception shapes our ecological ethics.
The plant itself is neutral.
Whether it becomes a symbol of destruction or a source of healing depends on the human context.
In that sense, Reynoutria offers a valuable lesson for our age:
that environmental judgment must go hand in hand with cultural understanding.
Closing
So, when we speak of “invasive species,” perhaps we should also ask:
invasive to whom, and under what values?
The Itadori that cracks British pavement is the same Itadori that flavors Kyoto’s spring cuisine,
and the same Oo-itadori that supports my aging knees.
Between pest and cure, between fear and nourishment,
lies the complexity—and the humility—of our coexistence with plants.
Thank you very much.