Is this statement applicable to any known plant/region combinations?
Plant species X, Y, and Z are truly indigenous to region R. Other "immigrant" species can be destroyed by drought or harsh weather, but these species will always be part of the region R.
(all species in question are "benign" - like wheat; please disregard climate change and other global disasters like nuclear wars).
PS. Background: I heard this statement (with specific X,Y,Z,R) attributed to a "leading botanist" (probably 20th century), but I don't really see how this can be true (my biology education ended in high school though; I am a mathematician by training).