The center recently listed 52 "unhealthy plants" that it says can lead to cancer if people are exposed to them over a long period of time.

"In general, plants with special smells are not appropriate for indoor decoration and for places with poor ventilation, particularly in bedrooms," Ye Ziyi, a botanist with the Shanghai Botanical Garden, said yesterday.

She said the center has been studying the effect that plants have on health since 1982. Some of the dangerous plants on its list - such as the redbird cactus and an euphorbia plant called Crown of Thorns - are easily found in local flower markets.

"People need to be careful when selecting plants to grow indoors in the winter time," Ye said.

She said, however, if plants are grown in rooms with good ventilation and not kept in bedrooms, the listed plants will not make people sick.

Botanists said some plants, such as aloe, can be grown to absorb harmful smells and purify air.

In the Caojiadu Flowers Market, it's not difficult to find stalls selling redbird cactus for around 60 yuan (US$7.43) each.

A salesman surnamed Huang commented: "It seemed that no one believes those beautiful plants can cause cancer."

Huang Zhihao, a local housekeeper, said: "I don't think the consequence of growing those plants will be that severe."

"Experts always like exaggeration," he said.