Botanical gardens also show individual plant species and help in their identification
Please see Ocimum canum of family Labiatae ( Lamiaceae) It has great medicinal potential including anticancer and radiation protection value. Its closely related to holy plant Tulsi (Ocimum sanctum)  of Indian mythology.

Botanical garden also maintains water plants in ponds.

Justus Liebig Universitat Giessen, Germany has one of the oldest botanical garden of Germany
The concept of botanical garden dates back from middle ages or even before. Kew botanical garden in UK one of the oldest . It provides a basic knowledge about plants.
What the manking has lost is time to stop and admire tne nature. Going away from nature has caused several life style diseases.