Aerial root
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"Pneumatophore" redirects here. It is also a name for the air bladder of the Portuguese Man o' War.
Aerial roots are roots that are aboveground. They are almost always adventitious. They are found in diverse plant species, including epiphytes also known as air plants, which includes the orchids, tropical coastal swamp trees such as mangroves, the resourceful banyan tree, the temperate forest Rata and Pohutukawa of New Zealand and vines like English ivy and irritating poison ivy.
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[edit] Types of aerial roots
This plant organ that is found in so many diverse plant families has different specializations that suit the plant habitat. In general growth form, they can be technically classed as negatively gravitropic (grows up and away from the ground) or positively gravitropic (grows down toward the ground).
[edit] Support aerial roots
In the case of the Banyan tree, also known as the strangler fig, the tree begins as a small aerial plant. Its roots grow down and around the stem of its host until it reaches the ground. The roots sprout branches along the way, and eventually when soil is reached, will absorb mineral nutrients and water. The roots eventually "strangle" the host tree and then the hollow cylinder of aerial roots serve as the banyan's trunk.
Non-parasitic ivy are vines that use their aerial roots to cling to host plants, rocks, or houses. Prop roots form on aerial stems and grow down into the soil to brace the plant, e.g. maize and screw pine.
[edit] Pneumatophores
These specialized aerial roots enable plants to breath air in habitats that have waterlogged soil. The roots may grown down from the stem, or up from typical roots. Some botanists classify these as aerating roots rather than aerial roots, if they come up from soil. This is a good example of the living nature of plant taxonomy, that different experts hold opposing views on the subject. The surface of these roots are covered with lenticels which take up air into spongy tissue which in turn uses osmotic pathways to spread the needed oxygen throughout the plant as needed.
[edit] Haustorial roots
These roots are found in parasitic plants, where aerial roots become cemented to the host plant via a sticky attachment disc before intruding into the tissues of the host. Mistletoe is a good example of this.
[edit] Propagative roots
Horizontal, aboveground stems, termed stolons or runners, usually develop plantlets with adventitious roots at their nodes, e.g. strawberry and spider plant.
Some leaves develop adventitious buds, which then form adventitious roots, e.g. piggyback plant (Tolmiea menziesii) and mother-of-thousands (Kalanchoe daigremontiana). The adventitious plantlets then drop off the parent plant and develop as separate clones of the parent.
[edit] See also
[edit] References
- UCLA Botany glossary page: Roots
