a specialized root of certain swamp plants, such as the mangrove, that branches upwards, rising above ground, and undergoes gaseous exchange with the atmosphere
2.
a polyp in coelenterates of the order Siphonophora, such as the Portuguese man-of-war, that is specialized as a float
a porous, woody, specialized branch growing upright into the air from the buried roots of certain swamp trees, as the mangrove, and providing access to the atmosphere
2. Zoology
a polyp with a gas-filled cavity in siphonophore hydrozoans, serving as a float for the colony