NATURE IN SHORT / A story of how Asian species of Kuzu came to invade U.S. soil

Kevin Short / Daily Yomiuri Columnist

A few days ago, I was watching one of those "Life After Humans" type shows on an educational channel. These shows develop scenarios about how the earth would change should humans be suddenly eliminated. This particular episode was set in the southeastern United States, and one terrifying scenario showed the city of Atlanta, Georgia, being attacked, overrun and eventually dragged into the ground by an incredibly aggressive vine.

The vine, of course, was none other than the ubiquitous kuzu, one of the most common roadside plants here in Japan. Kuzu and several closely related species are native to southeast and east Asia. Kuzu (Pueraria lobata) itself is found from central Honshu south through Kyushu and Shikoku. How this Asian species came to be attacking Georgia is a fascinating story.

Kuzu, called kudzu in English, was first brought to the United States in the late 19th century. Originally the vine was valued as an ornamental for training on shade trellises. Later, American farmers realized that livestock simply love it. A legume, kudzu is rich in protein and is considered an excellent livestock fodder. Still later, in the 1920s and 1930s, the vines were widely planted to prevent erosion and restore nitrogen in farm lands that has been overworked.

Kudzu soon developed a reputation as a "wonder plant." But like many so called wonders, the vine had an insidious dark side, which Americans were about to be made painfully aware of.

In its native habitat, kudzu is basically a colonizer of open, disturbed areas. A sun-lover, the vine grows quickly along fences, and twines its way up the sides of poles and buildings. In fact, so quickly does kudzu grow that in the American southeast it is sometimes known as the "mile-a-minute vine." Under ideal conditions the tip of a shoot can extend 30 centimeters in a single day, and up to 20 meters in a season. Although the kudzu does lose its leaves and die back somewhat in winter, the vine is really semi-woody, which means that much of the aboveground part survives and continues to grow the following year.

The secret to kudzu's phenomenal growth lies in its huge ternate compound leaves (sanshutsu-fukuyo). Each leaf consists of three leaflets that can be rotated 90 degrees on their axis. This feature allows the vine to maximize access to sunlight over a wide area. Interestingly, when the sun at high noon gets a bit too hot, the vine minimizes water evaporation by rotating the leaves so that only the edges face upward, a process which the Japanese refer to as Kuzu no Hirune, or the "kudzu's afternoon nap."

In addition to strong vines and efficient leaves, the kudzu also boasts an incredible underground root network. Energy is stored away in thick roots, and the network is constantly expanding by sending out new shoots and runners--a system that allows the vine to quickly spread out and cover an open field.

Nowadays, kudzu is considered to be one of the most destructive invasive plants in all the United States. Estimates place the total amount of kudzu-dominated land, centered from east Texas across to the Atlantic seaboard, at several million hectares. The vine disrupts the landscape, reduces biodiversity by forcing out native species, prevents forest regeneration, and is constantly invading railroad tracks and utility poles. Estimates of annual economic damage run in the hundreds of millions dollars. So devastating has kudzu become that it has earned another nickname "The Vine that Ate the South."

Kudzu has become a nuisance in some parts of Japan as well. In the suburban complex where I live, for example, the landscape maintenance teams are constantly fighting to eradicate the vine. In Japan, however, kudzu's spread is limited to highly disturbed areas. One reason is that in most places there is an army of equally tough native plants willing and capable of fighting for access to the light.

Traditionally, kudzu was considered a highly beneficial plant here in Japan. Some elderly farmers still remember the days when horses stoked up on kudzu leaves did most of the heavy plowing and carrying work. In some areas local women still weave baskets of kudzu vine; and kuzuko, a starchy substance extracted from the root, is used in the manufacture of kuzu-mochi and other traditional sweets.

Powdered kudzu root, or kakkon, is also an important element in traditional Asian kampo herbal medicine, administered to improve blood circulation and relieve muscle aches and slight fevers. A tea made from the root has also been used to treat mild diarrhea, and even to reduce cravings for alcohol. Kakkon-to, an herbal concoction containing kudzu root and various other ingredients, is prescribed for relief of upper body muscle stiffness, and to alleviate the symptoms of light colds and viral infections.

Kudzu is also appreciated as one of the famous aki no nanakusa, or "Seven Flowers of Autumn," celebrated in poems collected in the Manyoshu, Japan's oldest anthology of poetry, compiled in the mid-8th century. A member of the Legume Family (mame-ka), kudzu's peaflowers sport several shades of light and deep purple, with a single yellow spot at the center. The flowers bloom in long, spikelike clusters that project stiffly upward from the leaf joints. Often the flower clusters, which are in full bloom right now, are hidden among the leaves, and you have to poke around to find them.

The seeds of the kudzu vine are contained in hairy pods that form in mid to late autumn. These pods are light, and after falling can be dispersed on the wind, and also perhaps to some extent by clinging to the fur of passing animals.

Short is a naturalist and cultural anthropology professor at Tokyo University of Information Sciences.