Diellia were restricted to a particular spatially fragmented habitat type on the steep northern slopes of gulches. Diellia falcata, D. pallida, and D. unisora were growing on soil, whilst D. erecta occurred on soil as well as on old lava blocks and cliffs. Target ferns were found mostly in areas with a sparse ground layer and in the shade of the canopy. The natural vegetation was usually mesic lowland or mountain forest, dominated by Metrosideros polymorpha Gaud., and Diospyros sandwicensis (A. DC) Fosb. At the sites on Oahu, the vegetation was dominated by invasive Psidium cattleianum Sabine and Schinus therebinthifolius Raddi.