We introduce a novel approach for conservation of endangered plant species in which ex situ collections maintained in natural or semi-natural environment are a part of a complementary ex situ – in situ conservation strategy. We provide detailed guidelines for 1) representative sampling of the populations; 2) collection maintenance; and 3) utilization for in situ actions. Our approach is the first that explicitly takes into account ecologically significant (i.e. adaptive) variation of plants in both ex situ and in situ conservation actions. We propose that an important part of the conservation strategy is preserving both neutral and adaptive genetic diversity through a quasi in situ conservation approach. Finally, we demonstrate this approach using a critically endangered plant species, Iris atrofusca from the northern Negev, Israel.