Plant Profile: Mangroves By Craig Huegel Reprinted from The Understory, Oct.-Nov. 1998 (Illustration © Cathy Vogelsong) "Mangrove" is a term used to describe a botanically diverse group of salt-tolerant trees and shrubs that include 12 families and more than 50 species worldwide, in semitropical and tropical regions. While all of these plants are not closely related, they share four major adaptations to (1) loose, saturated soils, (2) saline habitats, (3) periodic tidal submergence, and (4) varying degrees of production of propagules instead of standard seeds. Four major factors limit the distribution of mangroves and determine the extent of their development. The first of these factors is climate. Mangroves are damaged by temperatures below freezing and are killed if freezing temperatures last for an appreciable length of time. Therefore, this group is limited to tropical and semi-tropical regions. They do not occur much north of Pinellas County on the west coast of Florida and it is rare to see one that has developed its full size potential. The second critical factor is salt water. Mangroves grow quite well in freshwater environments, however, mangrove systems do not develop properly in them. The main reason is competition. Salt water is very difficult to adapt to, and few plants are capable of growing in pure salt water. Mangroves become out-competed in freshwater conditions, but they win the race in salt. A third factor is tidal fluctuations. Tidal movements also are difficult to adapt to. Mangroves are capable of withstanding that constant fluctuation. In fact, they are the first plants to colonize the frontline of coastal areas left bare of vegetation. Worldwide, mangrove systems reach their greatest development in areas with the greatest tidal fluctuation. The final factor is wave energy. Although mangroves colonize the leading edge of coastal areas, they grow best in areas with low wave energy. High wave energy prevents establishment of their propagules, prevents the accumulation of sediments that improves growth, and is difficult for their shallow root systems to adjust to. Three mangroves are native to Florida. A fourth species, buttonwood (Conocarpus erectus), is not a true mangrove and will not be discussed below. It is, however, an important member of the plant community of the upland edge of mangrove ecosystems. Black mangrove (Avicennia germinans). Black mangroves have the greatest distribution of our three species. Although their best development occurs in frost-free regions of the state, they occur as scattered shrubs along the length of our eastern and western coasts. When fully developed, black mangroves can reach a height of about 65 feet. Its name comes from its very dark, scaly bark, evident on large trees. Its leaves are 2-4 inches long, elliptical, shiny green above and covered by short dense hairs below. The tree flowers in the late sprint to early summer and the clustered flowers are white. At one time, black mangroves were included in the verbena family, and the flowers have that verbena characteristic. I find that the easiest character to distinguish this mangrove from the others is at the soil level. It produces lots of root growths known as pneumatophores that arise several inches vertically from the soil beneath the plant and aid in oxygen transport. White mangrove (Laguncularia racemosa). White mangroves are found in Florida from central Florida coastlines southward. They are small trees that rarely exceed 50 feet in height. I find their leaves to be a distinctive feature that separates them from the other two species. White mangroves have noticeably rounded leaves that may be 3 inches in length. They also have two salt glands near the base and the underside of the leaves frequently are encrusted with salt. White mangroves do not have any type of root above the soil surface. Red mangrove (Rhizophora mangle). Red mangroves are the largest of our three species and the one that is most adapted to colonizing the outer edge where wave action is greatest. Although they may be found throughout the mangrove community, they are most abundant on that outer edge. An adult red mangrove may reach a height of 80 feet. It has grey bark and dark red wood. The leaf shape is similar to that of the black mangrove, but leaves may be up to 5 inches long. Red mangroves are most easily identified by their "prop" roots. These long, sinuous roots arise from along the trunk and branches and help to stabilize the tree in the substrate below. Red mangroves also produce pencil-shaped propagules that may be a foot in length. The mangrove featured on our chapter's t-shirt is a red mangrove.