As vegetative architecture and its main concepts (sequential branching, architectural models, reiteration) were born in the humid tropics, a long term study of the Juan Fernández flora and vegetation provided an opportunity to test whether or not those concepts remain valid in quite a different sort of environment. Robinson Crusoe is an isolated island of the South Pacific, at 33° South, having an oceanic temperate climate, a rough topography and a rich highly endemic flora. Through the architectural analysis of more than 50 species of ferns and seed-plants, it is established that, not only are the architectural concepts still valid, but that the 12 architectural models actually recorded are identical to those found elsewhere on mainlands, even if their taxonomic distribution differs. The reiteration ability is unevenly distributed: rare or absent in most of the endemics, it is extremely developed in the “pests” introduced from the mainland, Maqui, Zarzamora and Murtilla. It is shown that such a big difference in reiteration ability is likely to explain the threat that “pests” pose on endemics. The only possibility left to save the endemic flora seems to be the creation of a botanical garden on Robinson Crusoe Island.