Following the emergence of a new discipline, conservation biology, a new conservation tool has been investigated by the scientific community: the reintroduction of rare or endangered taxa. This article, which deals with two examples of the reintroduction of plant species carried out in France, illustrates how the rationality of such projects, frequently presented by their promoters as relying on the inscription of chosen taxa on lists of "protected species", turns out more to be socially constructed according to technical, strategic and communicational criteria. In this sense they are the products either of negotiation or crystallisation of various objectives. The observation of the construction of the reintroduced flower therefore allows us to observe the reciprocal influences between local networks and global networks.