These special roots, called pneumatophores or knees, develop in mangrove plants, i.e., plants growing in saline marshes. These roots grow vertically upward and are negatively geotropic.
Air enters these roots through minute breathing pores called pneumathodes, present on the tips of vertical roots. These plants include Rhizophora, Heritiera, Avicinnia, etc., and are found in Sundarbans of West Bengal.