Columbia subject headings:
Harvard subject headings:
Botany--America
Botany--Europe
Plant introduction--America.
Plant introduction--Europe.
Plants, Cultivated--America--Identification.
Plants, Cultivated--Europe--Identification.
Plants, Cultivated--Geographical distribution
Princeton subject headings:
Botany--America.
Botany--Europe.
Plant introduction--America.
Plant introduction--Europe.
Plants, Cultivated--America.
Plants, Cultivated--Europe.
Plants, Cultivated--Geographical distribution.