Lehmann conducted explorations in search of specimens of flora in the countries of
Ecuador and
Colombia over three decades, sending collected material to herbaria in
Berlin-Dahlem,
Kew, and
Saint Petersburg. In 1903 he led an expedition to
Popayán, Colombia, and passed through most of the provinces of Ecuador, in a search for orchids. He died reportedly of drowning in the Timbique River but his obituarist Kränzlin noted that it was not known if it was by "an unhappy accident or by malice". ==Family==