Engelmann met Schimper, Agassiz and Braun while a student, continuing the association with Agassiz and Braun in Paris. He met Gray after he emigrated to the U.S. Torrey stayed with him, while Parry became entangled with another botanical collector in an argument over a rose, which Engelmann tried to defuse (Parry having a long and close friendship with him). Hooker was one of his many correspondents.