This "laxative" is actually an endangered plant in China?

There is a plant that appears very frequently in film and television dramas. Many people have never seen this plant, but as soon as they hear its name, they know that it can cause humans, horses, cows, pigs and all kinds of animals to have diarrhea. It is croton.

Croton seeds contain a plant protein called crotonin, which is similar to some toxic proteins in castor beans. When cells come into contact with crotonin, they will die and hemolyze. When people take a large amount of croton, the stomach and intestines will move violently due to stimulation and produce secretions, thus "diarrhea". To put it bluntly, after croton poisons the human body, the rapid detoxification reaction of the digestive tract is the laxative principle of croton.

Croton fruit | Vinayaraj / Wikimedia Commons

How toxic is croton? An adult taking 1/4 drop of croton oil will have diarrhea 1-3 hours later, and taking 20 drops of croton oil can cause death. A horse eating 30 croton seeds may die 2-3 days later. So don't ignore the dangers of croton just because it plays a funny role.

Croton "Resurrection from the Dead"

The plant we are going to introduce today is a relative of croton: Hong Kong croton.

Croton hancei is a woody plant of the genus Croton in the Euphorbiaceae family. It is often a shrub but can also grow into a small tree. Its young branches and inflorescences have appressed star-shaped scales, and its leaves are papery and oblong-lanceolate. The racemes are terminal, with many male flowers growing densely together, and fewer female flowers, usually only one female flower at the base of the inflorescence. The genus name "Croton" of Croton comes from the Greek word "kroton (tick)", which refers to the tick-like shape of the seeds of this genus; its specific epithet "hancei" comes from its discoverer, Henry Fletcher Hance. The Chinese name indicates that it comes from Hong Kong, China.

Male flowers of Croton hongkongensis | A-Qiao HQ / Wikimedia Commons

There is a tortuous story about Croton hancei. In 1850, Hans collected a plant specimen on Hong Kong Island (the exact location is unknown). In 1861, British plant taxonomist George Bentham officially published it for the first time in the Flora of Hong Kong, and the type specimen was preserved at Harvard University. Since then, Croton hancei has a real name, and later the Lahan Seed Plant Name proposed its Chinese name as "Hong Kong Croton".

Scientific drawing of Croton (not Hong Kong Croton) | Rawpixel Ltd / Flickr

But since the publication, Hong Kong Croton has "disappeared" from people's sight, and it was once thought to be extinct. After that, almost no one collected Hong Kong Croton specimens. Some scientists could not help looking for Hong Kong Croton in Hong Kong, China, and reported that they had collected Hong Kong Croton specimens, but in the end they found that they were all misidentified specimens of Neoshirakia (Sapium) atrobadiomaculata. It was not until 1997 that Lin Yingwei, an employee of the Hong Kong Herbarium, collected a relatively special Euphorbiaceae shrub on Tsing Yi Island. Later, after identification by experts from the South China Botanical Institute, it was confirmed to be the Hong Kong Croton that had disappeared for a century and a half. Since then, Hong Kong Croton has once again entered people's sight.

Saving Hong Kong Croton

In fact, two plant specimens were collected in Hong Kong and Guangxi, China in 1929 and 1933 respectively, but they have been lying in the herbarium for more than half a century. It was not until the rediscovery of Croton hongkongensis that they were officially identified as Croton hongkongensis. Both are now preserved in the herbarium of the South China Botanical Garden, Chinese Academy of Sciences. The other specimen collected by Hans at Sun Yat-sen University was identified as Croton hongkongensis in 2001. The most recent specimen of Croton hongkongensis was collected and identified by Zhou Lianxuan in Taishan City, Guangdong Province in 2013, and is now preserved in the Kunming Institute of Botany, Chinese Academy of Sciences.

Croton hongkongensis, located in Shing Mun Herbarium, Hong Kong, China | Tequila / Wikimedia Commons

The distribution of Hong Kong Croton in the wild is very narrow. The only known stable wild population is on Tsing Yi Island in Hong Kong, China, with an estimated 1,700 wild individuals in 2006. Hong Kong Croton has been listed in the Red List of the World Conservation Union (IUCN) and its conservation level is Endangered (EN). The local authorities are protecting it in situ and actively conducting ex situ conservation research on Hong Kong Croton. Scientists obtained branches and seeds of Hong Kong Croton from Tsing Yi Island and propagated them in the experimental area through cuttings and sowing. The survival rate of cuttings is 80%, while the germination rate of seeds is 65%, which shows that the artificial propagation of Hong Kong Croton is quite successful.

There are currently only two known sites for artificial introduction and cultivation of Hong Kong Croton, one of which is located in Shing Mun Country Park. After successful cultivation in the experimental area, people will reintroduce it into a suitable natural habitat in the hope of establishing more wild populations.

Shing Mun Specimen Forest in Shing Mun Country Park, Hong Kong | Tequila / Wikimedia Commons

The traces of Hong Kong Croton are not limited to Hong Kong, China. It has also been found in Guangdong and Guangxi. However, currently only one stable wild population is known on Tsing Yi Island in Hong Kong. It is very likely that there are other stable populations in South China, which requires more exploration and discovery.