Tropicos
The Tropicos database is all of the nomenclatural, bibliographic, and specimen data accumulated in Missouri Botanical Garden’s electronic databases during the past 25 years. These data are publicly available on the above link. This system has over one million scientific names and 3.5 million specimen records.

Index Nominum Genericorum (ING)
This database is a compilation of generic names published for organisms covered by the International Code of Botanical Nomenclature. This is a collaborative project of the International Association for Plant Taxonomy (IAPT) and the Smithsonian Institution. It was initiated in 1954 and is considered complete to about 1990. Work is continuing to make the an up-to-date resource.