In China, plants could migrate south to survive. But in Europe, the Mediterranean blocked a southern migration. And in North America, plants were squeezed by the bottleneck going into Mexico.
China's complex topography—folded mountain chains run across the country, for example—also creates niches that allowed plants to evolve in isolation, Wen added.
"In that regard, it's not only a very interesting 'museum' that preserves a lot of ancient survivors, but at the same time many new things get created," she said.
As many as a sixth of Chinese plant species are used in traditional medicines, and many more are vital to Chinese diet and culture.
Scientists have derived an anti-malarial medication, artemisinin, from the shrub Artemisia annua. And a recent trial found the herb Houttuynia cordata is an effective treatment for severe acute respiratory syndrome (SARS).
Many plants, such as rice and soybeans, are staple food crops around the world. Others are familiar ornamentals such as lilacs, magnolias, forsythia, many kinds of roses, and rhododendrons.
But this crucial flora is threatened by a swelling Chinese population and higher rates of pollution, Raven, of the Missouri Botanical Garden, said.
(Related news: "China's Boom is Bust for Global Environment, Study Warns" [May 16, 2005].)
In 2002 the Global Strategy for Plant Conservation was adopted under the Convention on Biological Diversity, and in February 2008 China officially unveiled its own plant conservation strategy.
Raven is cautiously optimistic the plan will meet some success.
"China is becoming a relatively rich country and the government and people there are trying to do what they can to save what they have," he said.
James Wong is an ethnobotanist with the London-based Botanic Gardens Conservation International, which helped China develop its plant-conservation strategy.
The plan is the first on this scale anywhere in the world that is aimed at plant conservation, he said.
For example, within three years China hopes to revert nearly 37 million acres (15 million hectares) of farmland to forest. That's an area bigger than England, Wong noted.
"The amount of money and human labor they can put behind these initiatives is something that other governments simply could never hope to achieve," he said.
Other facets of the plan include a sweeping inventory and analysis of the country's plants, increased protection both in the wild and in botanic gardens, and a nationwide public-awareness campaign.
"Once it has decided on something, [China will] really go all out and do it in a big, big way," Wong said.
Still the task at hand is tremendous, Raven said.
For example, air in 97 of the 100 largest cities in China is among the most polluted in the world.
Over the next 20 years, these metropolises are expected to add another 250 million people.
(See photos of China's boomtowns.)
The growth threatens to eat up more farmland and further pollute the air, rivers, and streams.
Meanwhile, wild plants are being overharvested to supply the constant need for popular Chinese traditional medicine, as well as a burgeoning demand for medicines distributed around the world.
And while the conservation plan may look good on paper, "it's [the] early days," Raven said.
China's national park and nature reserve system is currently one of the most poorly funded per unit of land of any developing country, he pointed out.
"That leads to a situation—especially if [the parks] are not well integrated with the needs of the local populations—where the forests and natural resources of the area can disappear more rapidly than you would think," he said.
Wen said increasing public awareness about the value of these plants is critical to the success of the plant conservation strategy.
"The public, for the most part, does not recognize the importance of conservation in China," she added.
"People continue to cut firewood and dig medicinal plants without consideration for the next generation."
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