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Plant collectors in the Himalayas are 'forcing' a rare medicinal plant to rapidly evolve into a shorter form, and so could be pushing it towards extinction, according to research published this week.

Saussurea laniceps is a snow lotus that grows at around 4,000 metres above sea level. It is used in traditional Chinese and Tibetan medicine to treat headaches, high blood pressure and menstrual problems.

Collectors prefer tall specimens because they are thought to be more potent and are easier to find. But they harvest the plants — which only flower once — before they have had time to produce seeds.

This means that smaller plants are more likely to avoid being collected, and so reproduce successfully.

The US-based researchers, Wayne Law of Washington University and Jan Salick of the Missouri Botanical Garden, compared plants picked for medicinal purposes to museum specimen picked in 1872.

They also looked at S. laniceps growing on sacred Tibetan lands where the plant is rarely picked.

Recently-picked plants were about 15 centimetres tall, ten centimetres shorter than specimens from the early 1900s or plants growing on sacred land.

Shrinking snow lotus:
researchers believe that
human activities are
making S. laniceps smaller

The researchers also looked at a related snow lotus, Saussurea medusa, which is not collected, and found that its average height has not changed.

Although S. laniceps is mostly picked for its medicinal qualities, tourists also pick the flower because of its unusual appearance. The researchers conclude that the collectors' preference for larger plants is forcing the rare species to evolve into a smaller form.

They note that this process has been observed in fisheries as well, where a preference for larger fish means small fish are becoming more abundant.

However, if the smaller snow lotus plants produce fewer seeds, then human preferences could in fact be pushing S. laniceps to extinction, say Law and Salick.

Their study was published online this week by PNAS (Proceedings of the National Academy of Sciences).

Link to abstract of paper by Law and Salick in PNAS