Cypress trees grow along the banks of rivers, flood plains and near the edges of lakes and ponds. Their ability to grow in pools of standing water up to 4 feet deep make them unique among trees. Their roots are specially adapted to withstand the seasonal rise and fall of water levels in their native wetland habitats.
The knobby structures of the cypress tree roots that rise above the water level, or the 'knees' of the cypress tree, were once thought to provide the roots with aeration. But according to Gil Nelson, author of "The Trees of Florida: A Reference and Field Guide," this was disproved when all of the knees of a group of cypress were removed, and the cypresses did not decline in any way. The knees hollow out as they age, and the time of highest respiration of the knees is during floods and high water.
These roots stretch at least as far from the trunk of the cypress as the canopy, and sometimes farther. They are not buried in the ground. During floods, these roots float on the surface of the water, allowing them to continue to perform oxygen exchange when the rest of the roots are drowned. These roots may spring from the buttresses at the base of the tree, or directly from the main roots.
These structures, while technically part of the trunk, serve similar functions as roots--as far as anchoring. Buttresses flare skirt-like from the trunk of the tree, stretching farther the closer they get to the soil. They form a very wide base that moves water pressure during floods around the base of the tree, helping to keep it anchored. Buttresses also tend to hollow out as the tree ages.
Due to their aquatic environment, cypress trees have natural disease resistance. The roots do not rot in saturated soils, as happens with most other trees. While cypress tree roots still have the characteristics of all roots, the cell structures responsible for nutrient and water exchange are contained primarily on the specialized roots that have access to oxygen. This prevents cypress roots from being exposed to fungal and bacterial root rot organisms.
Forest and wetland trees have some of the strongest symbiotic relationships with beneficial fungi. Mycorrhiza, or 'root fungus,' are microscopic fungi that form a mat or even a sheath around the roots of cypress trees. They gather and store excess nutrients while they're available. When there are no longer sufficient nutrients in the surrounding soil for cypress roots, the Mycorrhiza gives up the nutrients to cypress roots in exchange for sugars the tree produces.