Hiking in Hong Kong usually involves carrying water, snacks and sunscreen – but health officials warn that if you forget food, local plants are not a sensible substitute. From mushrooms that can cause liver failure to commonly found species such as the lily of the valley, annual morning glory and the deadly graceful jesamine, there are plenty growing wild that are poisonous if eaten. Graceful jesamine is especially toxic, with the case of a Hong Kong woman who used the plant to poison her husband recorded in the medical journal The Lancet . It does not help that the yellow-flowered jesamine typically grows next to the hairy fig, a shrub whose root is commonly used as herbal medicine or in soups. However, unless you are an expert, identifying which plants are best avoided can be tricky, so the Hospital Authority Toxicology Reference Laboratory has published an online guide complete with pictures, listing the 117 most poisonous plants in Hong Kong. Dr Tony Mak Wing-lai, the lead author of Atlas of Poisonous Plants in Hong Kong – A Clinical Toxicology Perspective, is chief of service (pathology) at Princess Margaret Hospital and North Lantau Hospital, a deputy hospital chief executive at PMH, and service director (quality and safety) for Kowloon West Cluster. His team is preparing an article for publication in a peer-reviewed academic journal in the next year giving a detailed account of poisonings that have occurred in Hong Kong. Mak said that in the past 10 years “we came across 50 cases or so related to plant poisonings”, which equates to just three to five cases a year across the city’s 43 public hospitals. “So you can see that for an average doctor they would probably see one case in their lifetime,” he said. That statistic convinced Mak that a database for such rare cases would be very useful as “all the data and information out there is very patchy”. The guide also highlights the dangers surrounding the mushroom powder-cap amanita ( Amanita farinosa ), with six cases of amanitin poisoning recorded between 2013 and 2016. According to the guide: “The mushrooms were picked in Shing Mun Country Park, Tai Mo Shan Country Park and mainland China. All patients presented with gastrointestinal symptoms, three of them developed acute liver failure, and one of them required a liver transplant.” China’s most poisonous plant may also be deadly for cancer cells, scientists claim Lily of the valley ( Convallaria majalis ) is small, but just two sprigs is toxic, and cases of children being poisoned after misidentification of the plant, or accidental ingestion of its red berries, have been reported in Milan, Berlin and Finland. Meanwhile, just 1 to 2 grams of seeds from annual morning glory ( Ipomoea nil ) is enough to induce hallucinations, and more than that can lead to severe neurological disorders. Mak and his team of six editors, 10 contributors and three photographers took five years to complete the guide, and for senior medical technologist Chan Suk-san and scientific officer (medical) Lam Ying-ho, collecting samples presented its own set of risks. Chan once risked her life to look for the plant Arisaema erubescens , or dragon arum. “The plant is located near a cliff in Lantau Island where people are not recommended to go,” Chan said. “We needed to wear protective gloves and hold ropes to climb up and down. Finally we found the plant flowering along the steep slope.” For Chan, collecting samples often meant returning to the site of the plant more than once. Mak said: “We wanted to capture the plants in their flowering state and bearing fruits, so we needed to go to each plant twice to take pictures in different stages.” Ultimately, the best thing people can do is look but not touch, and certainly do not take anything home to eat later. “Avoidance is the key,” he said. “Don’t touch it, don’t pick mushrooms in the wild, especially for foreigners. They may have gone to pick mushrooms [at home], and those mushrooms may look like those in Hong Kong, but they could be completely different.”