The vascular plant herbarium contains about 2.5 million specimens, among which are about 30,000 nomenclatural types. For practical reasons, the herbarium has three main geographical divisions, the African, Belgian and General Collections. Each is then subdivided into pteridophytes, gymnosperms, monocots and dicots. Arrangement within the major units is alphabetical by families, genera, species and infraspecific categories.
The Herbarium Belgii contains 300,000 specimens from Belgium and Luxembourg. It houses many historical specimens and formerly private collections. It reflects the Garden's interest in the floristic exploration of our country. Plants cultivated in Belgium are included in the Herbarium Generale and dendrological specimens in a special collection.
The Herbarium Africanum houses about 1 million specimens from Sub-Saharan Africa, including islands in the western Indian Ocean such as Madagascar and the Mascarenes. It reflects Belgium's long-standing interest in Central Africa. Famous collectors include Frans Hens, Fernand Demeuse, Emile Laurent, Justin Gillet, Camille Vermoesen, Alfred Dewèvre, Jean Lebrun, Jean Louis, René Devred and many others. The main focus is on Central Africa (Congo, Rwanda and Burundi) but good general afrotropical coverage is attempted.
About 1 million specimens from the rest of the world are kept in the Herbarium Generale. It is here that most of the historical elements of the collection are kept, including the herbarium assembled by the Societé Royale d'Horticulture before 1870 including the collections of Henri Galeotti from Mexico and Peter Claussen from Brazil and the world famous Herbarium Martii, purchased by the Belgian government in 1870. Belgium's nineteenth century interest in the neotropics is reflected in historical collections such as by Funck & Schlim from Venezuela and by Pittier & Durand from Costa Rica. Nowadays, worldwide coverage is aimed at.
There are special collections such as of wood, dried fruit, and specimens kept in spirt. The following collections are also kept separately:
- Rosa herbarium of F. Crépin (kept in Crépin's arrangement)
- Rubus herbarium of J. Van Winkel (acquired 1997)
- Dendrological herbarium (cultivated trees & shrubs, mainly from Belgium)
- Teratological herbarium (anomalous structures & galls, mainly from Belgium)
- Large size collection (Palms etc.)