The living plant collections contribute to the botanical and horticultural research as well as to the education and conservation activities of the Garden. The greenhouse and outdoor collections together hold nearly 24,000 accessions of living plants belonging to about 17,000 taxa and 3,140 genera. During recent decades special attention has been made to the introduction of wild collected plantmaterial provided with detailed collection data.
Outdoor Collections
The outdoor collections accommodate about 7,000 taxa from all temperate regions of the world. A major part of them is planted in thematic collections open to the general public. Three systematic collections form the core of these plantings: the Herbetum (herbaceous plants arranged to the systems of Cronquist & Takhtajan), the Fruticetum (woody plants arranged to the system of Dahlgren) and the Coniferetum (gymnosperms arranged by genus). Nearly all hardy or 'half-hardy' genera are represented in these collections.
Another collection type is shown by the genera collections which give a thorough overview of the representatives of species and cultivars in the genera Quercus, Rhododendron, Hydrangea, Acer (Japanese & Chinese), Magnolia. Other developed thematic collections are the medicinal plants garden, the North American forest theme, the Mediterranean plants collection. A lot of collection plants are displayed in shrubberies and mixed borders all over the park. Rare or unusual tree species and cultivars are dispersed over the lawns and play the role of salt and pepper in the landscape dominated by indigenous tree plantations.
Other important collections of Sempervivum, Iris, Rosa, Paeonia and rare bulbs are also open to the general public. Special conservation collections are Mentha and Festuca holding the plants on which recent systematic revisions of these genera were based.
Well-represented plant families (on the whole outdoor collections) are Pinaceae (43% of extant species of the world), Aceraceae (42%), Betulaceae (39%), Hydrangeaceae (37%), Caprifoliaceae (33%), Cornaceae (31%), Cupressaceae (20%), Berberidaceae (16%), Ranunculaceae (14%) and Rosaceae (13%).
Woody plants from all these collections serve as objects for research on their hardiness and flowering behaviour. Some trees are really champion trees of Belgium and need special attention or care.
