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Brown said he thinks the demand in China is partially due to the growing urban middle class in the world's second-largest economy.
"Now you have the average Chinese citizen with disposable income looking for things that they can decorate their house with, and if you're living in a high-rise building, you only have a certain amount of space," he said, adding that sometimes a houseplant is the only bit of green in a person's home.
Chinese efforts to stop trade
Brown said buyers might not even be aware their plant was illegally pulled out of the ground in South Africa - and admitted the issue does not get people as worked up as something such as rhino poaching.
But he stressed that the trade is having devastating effects.
"A plant the size of my hand that's being smuggled to China could be 150 years old, and that's one of the plants that's setting seeds to replace itself in the ecosystem that's now been removed," he said.
There are various pages on the internet that offer succulent plants for sale, such as eBay and Etsy, and Chinese social media, according to CapeNature.
Scientific books on succulent types have also been translated into Mandarin recently, so people know what they are looking for.
Asked by VOA what the country is doing to try to end the poaching, the Chinese Embassy in Pretoria replied by email saying South Africa and China have been cooperating on combating such crimes.
"Over the years, the law enforcement departments of the two countries have always maintained close cooperation in cracking down on crimes such as smuggling ivory, rhinoceros horns and rare plants. Our smooth cooperation has produced fruitful results, especially in intelligence sharing, evidence exchange and arresting suspects," the embassy said.
Additionally, the embassy said, Chinese diplomatic missions in South Africa have repeatedly reminded Chinese citizens and tourists in South Africa to avoid picking wild plants at will.