The few foreign visitors who came to my ancestral home Dali in Yunnan in the 1980s broadly fell into two types. The first ones were people who dressed in formal suits and stayed at the most luxurious hotels – always accompanied by an English-speaking guide and driven around in chauffeured cars. The second type, however, was more interesting: carefree, young hippies clad in colourful clothes with unkempt long hair. They holed up in cheap guest houses, mingling with locals and venturing into the hills and woodlands, seemingly looking for something.

With my curiosity piqued, one day I summoned enough courage to ask one of them what they were doing. A man, said to be from California, gave me a mysterious grin and said: “We are looking for the magic plant ‘faiyezi’ (flying leaves).” I asked my botanist uncle what ‘faiyezi’ was. He laughed hard but never gave me a straight answer.

Many years passed before I realised what those visitors were searching for: marijuana. While peoples in Yunnan began to cultivate cannabis some 6,000 years ago, the modern marijuana industry started in the land where my visitor came from: the United States. It was no coincidence that he and hundreds of others travelled halfway around the world to Dali in search of the magic plant. Unbeknownst to either of us at the time, their journeys would lead to an intriguing evolution of the plant that is still unfolding today.

On April 20 when pot smokers around the world celebrate their hallowed “Weed Day”, the mood this year would be quite upbeat. In recent years, there has been a sea change in public attitudes towards cannabis in the West. More and more countries have legalised or decriminalised the recreational use of marijuana.

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Ironically, in Asia where cannabis cultivation first began, cannabis laws remain the strictest. China will probably be the last country to relax such laws because of its painful history with drug use. But even here, the story is not straightforward. China is by far the world’s largest cultivator of industrial cannabis, or hemp, and a leading researcher on the medicinal use of cannabis, accounting for more than half of the patents filed globally last year.

Let’s go back to the evolution of marijuana in America for a minute.

Few policies have backfired as spectacularly as the White House’s war on cannabis in the 1980s.

Smoking marijuana was always illegal in the US, but the law was loosely implemented throughout the 1960s and 1970s. Cannabis culture spread fast and wide thanks to the hippie movement and was on the verge of social acceptance. In 1972, US president Jimmy Carter even proposed to decriminalise marijuana. His point man on drug policy, Peter Bourne, openly smoked it.

Things took a sudden turn when Ronald Reagan came to power. Reagan and his wife Nancy crusaded passionately against marijuana, making it the focal point of America’s war on drugs. Marijuana was listed together with heroin and cocaine as the most dangerous drugs – even though there was no evidence suggesting that its effect could be anywhere as hazardous as the other two.

To this day, there is no single proven case of death caused by marijuana overdose. The drug dependency rate of marijuana is low. Only 9 per cent of marijuana users will develop withdrawal syndromes after they quit, on par with caffeine. By comparison, the dependency rate for tobacco is 32 per cent, alcohol 15 per cent and cocaine 17 per cent, according to a study by the US National Institute on Drug Abuse based on samples of 8,000 people.

Yet throughout the 1980s till 2000, the lion share of the US government’s anti-drug efforts was spent on battling marijuana use. Nearly 50,000 American citizens were jailed solely for marijuana-related crimes – higher than any other drug offence. Doctors were told they could not even talk about the potential medicinal use of the plant. Today, many are still puzzled by the intensity and single-mindedness in demonising cannabis. Some believe that its close identification with the hippie culture made it a trophy target for political conservatives who resented against the liberal 1960s.

Before 1981, most of the marijuana smoked in America was grown in Mexico. These were seeds of cannabis sativa, an equatorial species that could not set flowers north of the 30th parallel, meaning that it was difficult to grow in most parts of the US. Reagan’s war on marijuana, and Mexican drug cartels’ discovery that cocaine and heroin had much higher profit margins, stopped the flow of marijuana across the border.

Thousands of American hippies embarked on the “hashish quest” through Asia to search for a type of cannabis that would flower farther north. My first encounter with an American was a by-product of this big adventure.

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Eventually they found their holy grail in Afghanistan and returned with seeds of cannabis indica – a stout, frost-tolerant species that can flower as far north as Alaska. The indica is exceptionally potent, although its taste is harsher and its highs more physically debilitating than those of sativa. Many growers soon started crossing the two in the hope of producing something that would combine the most desirable traits of each plant. The result was a great revolution in cannabis genetics.

The new sativa/indica hybrids have the smoother taste associated with the best sativa and the powerful potency and hardiness of an indica. Today, these hybrids – including Northern Lights, Skunk #1, Purple Haze, California Orange and Pineapple Express – are regarded as the benchmarks of modern marijuana breeding.

Despite the sweeping ban by Reagan’s government, the growth of the plant expanded in the US. In 1982, the White House was embarrassed to find that the amount of domestic marijuana was bigger than its official estimate of total American crops. The US government began to fly aerial reconnaissance missions to spot marijuana farms. This forced the growers to move indoors. There, they kick-started a second revolution in cannabis genetics.

By growing cannabis in greenhouses, growers could precisely manipulate water, nutrients, light, carbon dioxide and heat. This made it possible to produce “Frankenstein” species that are small in stature but have extremely high yield and potency. The concentration of Tetrahydrocannabinol (THC), the principle psychoactive compound in marijuana, ranged from 2 per cent to 3 per cent before the crackdown in 1980s. Most of the natural cannabis species found in Yunnan, for instance, has a THC level between 1.5 per cent and 3 per cent. But in the greenhouses, growers started breeding marijuana with THC levels above 15 per cent.

Nowadays, THC levels in the range of 30 per cent are not unheard of. The China Yunnan, an indica-dominant hybrid strain, boasts a THC level of 15 to 19 per cent. It is much more potent and powerful than its natural ancestors. By 1987, all these various techniques had evolved into a state-of-the-art indoor growing regimen that came to be known as the Sea of Green (SOG). Today SOG has become the “industrial standard” for marijuana growers around the world.

Instead of ridding the world of a mild psychoactive plant that has been used by humans for thousands of years, Reagan’s war on marijuana became the greatest catalyst in the plant’s history and gave birth to the modern marijuana industry. Ironically, as American states now begin to legalise pot, the plant has been made much more potent and powerful since the crackdown.

These developments also shaped the plant’s story in Asia.

For millennia, cannabis has been an integral part of Chinese agriculture. One of the earliest written records of cannabis cultivation was found in China, written on turtle shells about 4,744 years ago. Its cultivation began at least 1,000 years earlier. Most of the Chinese cannabis, or hemp, belonged to a sativa strain low in THC – under 1 per cent. It was one of the five major agricultural crops – together with millet, sorghum, beans and rice – in ancient China.

Hemp produces strong fibers that are ideal for textile, rope and paper making. Some sativa strains, particularly those from Yunnan and Guangxi, have stronger THC. These are widely used as medicinal herbs. Entries of medical lore on cannabis are found in ancient text like Pen T’sao Ching – an influential Chinese pharmacopoeia written 1,800 years ago. It states that cannabis seeds have wonderful effects on curing many diseases such as dementia.

Because of the opium war, “dupin (poisonous stuff)” is stigmatised in modern Chinese culture. It is associated with national humiliation and foreign aggression. Chinese authorities and society took a very stern view on the use of dupin. But since cannabis was seldom used for recreational purposes in China, it was initially not considered a drug. Cannabis farms were particularly commonplace in Yunnan and Guangxi. While most of these grew industrial hemp, many ethnic minorities did include the more potent sativa strains in their diet. It was also widely used in their religious practices, with some believing it could give the power of divination when used together with ginseng.

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In 1985, China became a signatory of the International Drug Control Conventions. Under the heavy influence of the US, cannabis was included as one of the major banned plants. The Chinese government followed suit and started to crack down on marijuana. This caused a lot of confusion and even conflicts. In Yunnan, the provincial government initially confused drug cannabis with industrial hemp (technically, they do belong to the same species). Until the late 1990s, the growing of cannabis for any reason was prohibited. Many local farms and ethnic minorities bitterly complained about the blanket ban. Meanwhile, cannabis – wild or cultivated – continued to flourish in most parts of the province.

Chinese authorities soon realised that for the prohibition to work, they needed to “separate gold from sand”. In the late 1990s, the provincial government began to allow cannabis (hemp) cultivation. All the seeds had to be approved by the provincial academy of agricultural science. These seeds were genetically selected for low THC (below 0.3 per cent). In 2001, the government started to actively promote cannabis cultivation. To avoid confusion, the cannabis was renamed from “dama” to “huoma”.

Today, cannabis has become a multibillion-dollar industry in Yunnan. Cannabis farms spread to 13 prefectures and 38 counties throughout the province, producing more than 50,000 tonnes of sativa seeds annually. In 2012, industrial cannabis was listed as a priority project by the provincial government. The authorities even set up a 10-billion-yuan (HK$11.3 billion) industrial cannabis fund for research and promotion. Yunnan now boasts the world’s largest cultivation of industrial cannabis (hemp).

Unlike in the US or Japan, China did not ban research on cannabis for medical purposes. Of the 606 cannabis-related patents filed worldwide, China accounts for 309 of them. One key compound in cannabis is cannabidiol – proven to be effective in curing dementia, seizures, depression and Parkinson’s disease.

Exacting pure cannabidiol from cannabis is extremely difficult, as it is often mixed with THC. In 2014, Chinese researchers in Yunnan successfully achieved high-purity cannabidiol exaction (95 per cent) from sativa seeds. It has built the world’s first and only industrial centre to produce cannabidiol in large quantities. In 2015, China began to export cannabidiol to Europe.

Even the military began to take interests in cannabis. There are reports of military-related pharmaceuticals experimenting with cannabis extracts to produce drugs that could help soldiers “to overcome battlefield anxiety and depression”. Industrial insiders estimated that the cannabis industry would grow into a trillion-dollar business in the next decade.

The success story of Yunnan did not get lost on its neighbours. In December last year, the Thai government announced that it would allow six provinces in the north to grow industrial cannabis, copying the Yunnan model.

There are few if any plants that have undergone a more drastic genetic evolution as cannabis in modern history. For good and bad, seems certain to remain with us for centuries to come.

Chow Chung-yan is executive editor or the South China Morning Post, overseeing daily print and digital operations

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