Photo/Illutration Digitalis plants grow in the wild on a hill in Tochigi Prefecture. (Provided by Takayuki Kono)

The beauty of the pink and purple carpets of digitalis flowers increasingly seen on hillsides in Japan conceals a potential menace to ecosystems and even human health.

The flowers, which blossom in early summer, were originally a garden species native to Europe. The perennial plant is also known as a poisonous herb.

The Environment Ministry has not listed digitalis on its watchlists of invasive alien species, so circulation and marketing of the plant is allowed in Japan.

Takayuki Kono, a Yokohama-based photographer, was gathering information on other invasive alien plant species in 2021 when he learned that digitalis was growing in the wild in the country.

After checking news reports, websites for mountaineers, personal blogs and other resources, Kono found records showing that digitalis was growing naturally in more than 30 prefectures in 2006 or later.

There were even photo spots for the plant.

“Perhaps digitalis came under the spotlight because they happen to be attractive to the eye,” Kono, 63, said. “There could be other similar cases.”

The photographer said he notifies local governments and museums in areas where he learns that digitalis is growing in the wild.

Typically grown for ornamental purposes, digitalis can reach heights of more than 1 meter. It is also called foxglove because of the appearance of its flowers.

The plant contains such toxins as digitoxin. Ingestion can cause humans to vomit, feel dizzy and even die.

Digitalis plants in Japan were likely initially grown in residential yards in woodland areas and then spread into the wild. In other cases, the plant’s seeds may have been carried to the wild on humans or their clothing.

Digitalis breeds in cool climates, so its distribution could invade the breeding areas of valuable alpine and other plant species that are largely out of human eyeshot.

Deer have caused serious overgrazing problems across Japan, but they do not feed on digitalis. The poisonous flower could thrive while other native plants are eaten up by the animals.

Digitalis has yet to be designated a statutory “invasive alien species” by the Environment Ministry. Nor is it included in the central government’s broader “Invasive Alien Species List of Japan” of 2015.

Some local governments have taken matters into their own hands.

Wakayama Prefecture has designated digitalis an ordinance-based “species to be controlled.” The prefectural government has been working since 2019 to eradicate the plant in the Ryujin-mura district of Tanabe.

“We decided to start sooner rather than later because doing so is the golden mandate of measures against any invasive alien species,” said an official with the prefectural government’s office for the natural environment.

About 10 years ago, the village of Tenkawa, Nara Prefecture, started asking participants of its nature observation sessions and training courses for nature guides to uproot any digitalis.

“The plant is so tough, but some people who knew the situation in the past are saying that things have slightly improved,” a village official said.

Yoshinobu Hashimoto, a senior researcher with the Museum of Nature and Human Activities, Hyogo, a prefectural facility in the city of Sanda, is an expert on invasive alien plant species.

“There is a need to quickly gather basic information on measures (to halt the spread of digitalis plants), such as what volumes they are circulated in, where they are planted, how they are distributed geographically and what methods are being used by front-line workers to get rid of them,” Hashimoto said.

He said it is not always easy to prompt people to remove invasive alien plants that have beautiful flowers, even when they pose a threat to ecosystems.

“It is essential to issue stronger warnings, including using a legal framework,” Hashimoto said.

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