Lobelia niihauensis, a member of the Campanulaceae (bellflower) family, is a prostrate branched shrub. Each branch ends in a rosette of leaves which are 7 to 15 cm (2.8 to 6.9 in) long and 0.7. to 1.8 cm (0.6 to 0.7 in) wide. Magenta flowers are clustered at the ends of branches and produce an egg-shaped capsule 6 to 8 mm (0.2 to 0.3 in) long with many small brownish seeds.