The species represented in the Cadé Herbarium seem to originate from a cultivated collection. The collection consists of many species grown in medicinal gardens. Only part of the species occurred in the wild in the Low Countries, while some species were of Mediterranean origin and four species even have an American origin. The Mediterranean plants could have been cultivated in the Low Countries (in pots in the garden and taken inside or covered with leaves or mulch in winter) or could have been sent to him by traveling acquaintances or foreign resident apothecaries. The latter could also explain the collections with annotated German names. Another explanation for those German names could be that the plants were cultivated in a monastery from an order that originated in Germany.
In the 16 th century some courtyards and botanical gardens existed already. The most famous being the botanical garden of Peter Coudenberg / Pieter van Coudenberghe (1517/18–1594?), established in 1548 and destroyed in 1585. It was first assumed that this Peter Coudenberg made the current Herbarium, due to the initials PC on the first page of the Cadé herbarium (Stafleu & Cowan, 1976). Although the list of plant species that occurred in the garden of Peter Coudenberg shows some resemblance with the species incorporated in the Herbarium (Vandewiele, 1993), many occur under another taxonomical or local plant name, so it is unlikely that they share a common ancestry. Furthermore, none of the handwriting seems to match that of Peter Coudenberg.
Another possible source could have been the Hortus Botanicus at Leiden, but comparison with the plant species cultivated by Clusius (1594) show many dissimilarities. Moreover, no references to Cadé in the correspondence of Clusius have been found to date (pers.com Dr. F. Egmond, Clusius project, Leiden University).
Following the clue that Petrus Cadé could have been working in a small hospital or that his collections originate from an 'Artsenij Hof' (a medicinal garden used by a physician), a search was conducted concerning the monasteries and small hospitals of Brabant in the period 1550 -1600. This proved to be a very difficult query, due to the turbulent political situation in the Low Countries at that period (see Context). To date, no archives have been found that show traces of a common ancestry with the Petrus Cadé Herbarium.