Humboldt started his investigations in the field of plant geography by asking questions about the connection between the history of plants and that of mankind. During his American journey, Humboldt developed the concept of plant physiognomy: Main morphological forms determine the character of different types of vegetation. In the “Tableau physique des Andes et pays voisins”, which was also designed during the journey, the geography of plants is part of a global geoscientific research project. During the 1820s, Humboldt developed the numerical method of botanical arithmetic. This concept, as well as the–ultimately abandoned–project of a <ref xmlns="http://www.tei-c.org/ns/1.0" target="https://edition-humboldt.de/themen/detail.xql?id=H0002731&l=en">new edition of his “Essai sur la Géographie des plantes”</ref>, were part of a broader vision of plant geography on a global scale.