Plant This! Not That!

We adore wetlands. They clean our water and air, sequester carbon dioxide, and are home to more biodiversity than any other ecosystem on the planet. However, their wet soil conditions are less than ideal for most plants because of limited air sources. 

Arlington Wetlands, Photo: Mike Matney

Plants need carbon dioxide but also require oxygen for plant growth.  The water in wetlands causes the necessary oxygen for root growth to bubble out of the soil, and microbes eat the remaining oxygen. Luckily, plants have evolved adaptations to survive these inhospitable conditions.

Wetland Trees and Shrubs

If you’ve ever seen a bald cypress tree near a pond, you probably noticed elevated roots, known as pneumatophores (more commonly called knees), that rise above the surface of the water and specialize in gas exchange.  Wetland trees typically have a large number of small openings on the bark, called lenticels, on their twigs for increased gas exchange.  The trunks often have swelling or large folds near the base, known as buttresses and fluting. These trunk features help anchor the trees in the loose wetland soils. Wetland trees can also sprout roots further up the trunk to take up oxygen during periods of high water.  Trees with these adaptations can live happily with wet feet where other tree species cannot survive.

Red-Barked Dogwood (Cornus alba) in autumn


Flowering Plants and Grasses

Flowering plants and grasses use different strategies to transfer oxygen to root systems in oxygen-deficient wetlands.  Wetland plants have special tubes that allow air to flow easily from the above-water parts of plants down to root systems. Other wetland plants stretch their stems above the water level.

Red cardinal flower (Lobelia cardinalis)  in a wetland