Last month, while looking for lilies in a Colombian tributary of the piranha-packed Orinoco River, he jumped from plank to plank in the pitch dark at 4 a.m. to get to a floating pontoon. “It’s not that I am that daring,” said Carlos Magdalena, a research horticulturalist at the Royal Botanic Gardens, Kew, in London. “These situations just arise, and they are not like Superman extreme. Sometimes it’s more Peter Sellers than Indiana Jones.” ..he is also known as “the plant messiah,” as anointed by a Spanish newspaper in 2010, for his work rescuing several plant species from the...