The BBC's Rupert Wingfield-Hayes in Tokyo says Japanese media have cited anonymous sources as saying that Mr Aratani had been on a rare visit to the plant to meet senior executives from partner companies.

BBC: Algeria siege dead and survivors flown back to Japan

He said it was "very rare" that a plant-eater would sport sharp-edged, enlarged canines.

BBC: Dwarf 'vampire' dinosaur was a plant eater

The rare leaf is a part of the tobacco plant called the medio tiempo, taken from the upper leaves of the plant, but which not every plant produces, making it rare.

CNN: STORY HIGHLIGHTS

SEARCH, a non-profit body in Tucson, collects wild plant varieties, including rare or unknown chiles.

ECONOMIST: A brief history of chile cuisine

Francoise Barbira-Freedman, a medical anthropologist at Cambridge University, described how she discovered the remedy, which is derived from the rare Acmella oleracea plant, while visiting the tribe in the rainforest.

BBC: Herbal dental remedy a 'potent anaesthetic'