From Plant Press Vol. 17 no. 2, April 2014.
By Ashley N. Egan
Plants can eat things – large things! Well – figuratively anyway. One of the hungriest plants in the United States is kudzu (Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & Almeida), a large leguminous vine that can grow up to 60 feet in a growing season, and is often seen engulfing whole structures and damaging forest margins. I first became interested in kudzu while working as a postdoctoral fellow at Cornell University studying the phylogenetics and systematics of Phaseoloid legumes, a group of nearly 2,000 species mostly comprised of vines. During a phylogenetic investigation of subtribe Glycininae, we confirmed massive polyphyly within Pueraria. It was then that I determined to study the genus.
Kudzu was introduced into the United States in the late 1800s and touted by the U.S. government as an excellent forage crop and soil erosion solution. However, after escaping cultivation, efforts soon turned from advocacy to eradication, but with little success. Even today, kudzu continues to make headway across the American landscape, now occupying more than 15,000 square miles, costing the U.S. government hundreds of millions of dollars annually in control measures.
This invasive species, along with 20 or so congeners, is native to Southeast Asia where it grows from sea level to around 2000 m in elevation in temperate and (sub)tropical climes. To investigate the introduction history and genetic diversity of kudzu in the U.S. as compared to native ranges, and to decipher the extent of polyphyly in the genus, I set out on my second Asian expedition to collect Pueraria.
On 1 September 2013, just two weeks after starting as an Assistant Curator at the Smithsonian Institution, I and my Ph.D. student, Matthew Hansen, flew to Beijing, China – the first stop on a three month expedition that would cover three countries. In Beijing, we met up with Liu Luxian, a first-year Ph.D. student from Zhejiang University studying in Chengxian Fu’s lab. After two days of preparations, we boarded a train towards Anshan, Liaoning Province, one of the most industrial cities of China, at the northern edge of kudzu’s native range. There, we collected our first kudzu population of the season in the Qianshan Mountains. After returning to Beijing by train and preparing our specimens for travel, we flew to Xi’an, Shaanxi province for the second leg of the expedition.
Our expedition team usually consisted of at least four people, with a driver, translator, and various number of field assistants in tow. In Xi’an, we were met and assisted by a crew from Northwest University, including Ni-Shifeng, who was indispensable in helping us prepare for our next foray that would include over 750 miles of collecting sites spread across the province. Kudzu grows quickly both clonally and through seed, spreading over the landscape in large patches that can be miles long. To ensure that we were collecting separate individuals and not clones, we sampled ‘by car’ – collecting one individual every 1-2 km. Over the next five days, we collected ~150 individuals from seven roughly-defined populations with individuals at least 1 km from each other and each population about 100 km apart.
From Xi’an, we flew to Changsha where the next leg of our journey took us nearly 1000 miles across the lush landscape of Hunan province. Along the way, we encountered ancient temples, floating mountains, and quaint villages. In one locality, we collected a variety of kudzu that had most likely been cultivated for hundreds of years within the ancient village of Au Tau, south of Wugang, Hunan, China. On several occasions during the expedition, we were approached by curious villagers who, learning of our interest in kudzu, would launch into the virtues and uses of the plant.
The economic significance of Pueraria species has been documented since ancient times, with kudzu mentioned in Chinese literature dating as far back as 500 B.C. (Econ. Bot. 28: 391-410; 1974) and Japanese literature around 600 A.D. where kudzu was said to be a source of fibers for paper, clothing, cordage, and construction materials. Various species have been heavily tapped as starch sources anciently and in present day cultures across Indo-China and Southeast Asia (The Book of Kudzu, a culinary and healing guide, 1977). Pueraria species have long been used in traditional Chinese herbal medicine (Pueraria: The Genus Pueraria, pg 59-69; 2002) for treating numerous complaints, including skin rashes, dysentery, alcoholism, and hypertension. For thousands of years, Chinese herbalists have prescribed flower and root concoctions of kudzu as a means of curing alcoholism. Preclinical studies showed extracts to significantly decrease free-will consumption of alcohol by the golden hamster, an alcohol-craving rodent, via the action of daidzin, an isoflavone (PNAS 92: 8990-8993; 1995), as well as to decrease the effects of alcohol hangovers (Alcohol Clin. Exp. Res. 18: 1443-1447; 1994). Human trials of kudzu preparations have been conducted (Pueraria: The Genus Pueraria, pg 159-179; 2002).
From Changsha in Hunan province, we were to fly to Guangzhou, the economic center of Guangdong province in the South of China. Enter Super-Typhoon Usagi, the first of five typhoons that would in some way impact my three-month expedition. Just hours before we were to land in Guangzhou, super-typhoon Usagi was bearing down on Hong Kong. Because of the intensity of this storm (equivalent to our category 5 hurricane) and the potential for widespread flooding, road washouts, and disruptions, we decided to reroute and spend our remaining time in southeastern provinces. From Changsha we flew to Hangzhou where we were met by our collaborator Fu.
Over the next two weeks, we made three forays into neighboring provinces, taking a number of Fu’s students with us for the ride. Our first foray was near the Huangshan Mountain range in Anhui province, which includes the famed Yellow Mountain, one of China’s most important heritage sites and now designated as a UNESCO world natural and cultural heritage site. This area provides protection to a number of threatened plant and animal species. We were hoping to collect Pueraria stricta based on historical localities from the Hangzhou herbarium. This would represent a disjunct population from a species I had tried and failed to collect in the wild in 2012. Alas, we failed yet again.
Most of our collections in China were Pueraria, with the hope of collecting samples of every species in the genus. Perhaps the most interesting Pueraria we found in China was on our second foray out from Hangzhou, a loop that included collecting in three provinces over the course of over 1000 miles. After four weeks in the car, the endless movement as the landscape skimmed by became monotonous. So much so, that at one point I began to see ghosts – phantom images of what I swore was a white kudzu. We were moving fast along the national highway where we couldn’t stop to collect so I didn’t think anything of it. I had never heard of a white kudzu. I was seeing things, surely. But after the fourth such encounter, I realized I was in an area where I was allowed to collect – I loudly yelled “Ting!” Ting means ‘park the car’ in Chinese and was the universal signal for the driver to pull over as soon as possible. I or my student had yelled Ting over 500 times on this trip. I jumped out of the car and – sure enough – a white variant of kudzu was staring me in the face. We had likely found a white form of Pueraria tonkinensis Gagnep., a synonym of P. montana (Lour.) Merr. described from Jiangxi province.
Our third and final foray was to Zhoushan, a collection of islands off the east coast of China in the East China Sea. These islands were an important collection locality as they are the closest to Japan, where kudzu is also native and widespread. This foray was threatened yet again by not one – but two typhoons – Fitow and Danas. We ended up cutting our trip short by a day as we raced back to the mainland to avoid the storm surge from Fitow. Danas had pushed Fitow inland towards Hangzhou, just before turning towards Japan, where it would eventually slam into Fukuoka, my next destination. The next three days were spent inside as rains pummeled the city, causing localized flooding and road closures. After a successful five weeks in China in which we had collected nearly 500 samples each separated by no less than 1 km, our journey was coming to an end. The next morning I was to put my student on a plane back to the U.S. while I was to continue on to Japan to collect kudzu across the three largest islands. I went to sleep wondering if my flight was going to be canceled, dreaming of collecting kudzu in gale force winds and torrential downpours. Little did I know how soon that nightmare would become reality…but that’s a story for another time.