pneumatophore

pneumatophore, specialized lateral root that grows upward from the primary root system of certain wetland trees and shrubs and protrudes above surrounding mud or water to promote oxygen intake and gas exchange. These structures are perforated with small openings called lenticels, which allow air to enter and pass through spongy tissue to the submerged roots, facilitating root respiration in wet and often saline environments.

Pneumatophores are characteristic of many mangrove species—such as Sonneratia (family Lythraceae), white mangrove (Laguncularia racemosa; family Combretaceae), and black mangroves (Avicennia species; family Acanthaceae)—that grow in tidal mudflats and other coastal environments. Exhibiting negative geotropism (growing against gravity), mangrove pneumatophores typically rise several centimeters above the low-tide level. Similar structures also occur in other hydrophytic trees (growing in waterlogged soils), including bald cypresses (Taxodium distichum) and water tupelo (Nyssa aquatica).