Lobelia niihauensis is currently found on the eastern Wai`anae Mountains, O`ahu and Kaua`i. As the name suggests it is known to have been present in Ni`ihau however, no plants are currently known from there, and collections from Ni`ihau are known only from herbarium specimens.
This species grows on exposed dry to mesic cliffs from 125-725 m.
The genus Lobelia contains around 350 species and has a cosmopolitan distribution meaning that it is found throughout the world. There are thirteen endemic Lobelia species in Hawai`i. The Hawaiian species may represent two independent colonization events as the species with blue or magenta flowers (including L. niihauensis) are thought to be closely related to tropical Asian species and those with crimson, yellow, or greenish white flowers are thought to be more closely related to Brazilian or eastern Asian species.
(Endangered and Threatened Wildlife and Plants; Revised Determinations of Prudency and Proposed Designations of Critical Habitat for Plant Species From the Islands of Kauai and Niihau, Hawaii. Federal Register Volume 67 (18): 4089-4098)
(Wagner, W. L., Herbst, D. R., and S. H. Sohmer. 1999. Manual of the Flowering Plants of Hawai`i. Revised Edition. Volume 1. Bishop Museum Special Publication 97. University of Hawai`i Press, Bishop Museum Press, Honolulu, Hawai`i.)