How Red Mangroves Grow

In the wild, red mangroves may mature into low, bushy, round-topped trees growing up to 30 feet in height with many aerial roots, or trees up to 80 feet in height with a straight trunk and a narrow top or head.

The red mangrove is primarily self-pollinated. Germination takes place while the embryo is still attached to the parent tree. The flowers of red mangrove trees are pale yellow with four petals, about an inch in diameter, in a cluster of two or three. The fruit is a brown, leather-like berry, about an inch long. Out of the end of the fruit hangs a seed which germinates while still attached. These long, spear-shaped seeds are called propagules. They may grow in place for up to three years, reaching lengths of up to 36" before breaking off from the fruit and falling into the water.

These seedlings travel in an unusual way. In salt water they lie horizontally and move quickly. On reaching fresher (brackish) water they turn vertically, making it easier for them to lodge in mud. These floating seedlings can survive, in a state of suspended animation, for up to a year in the water. Once lodged in mud they produce roots and begin to sprout.

After sprouting, the first years of growth involve additions to the foliage without any major change in height. Prop roots appear by the third or fourth year of growth, serving as anchoring and breathing organs. These seedlings and saplings have a very low survival rate thanks to the stresses of salinity, flooding, insufficient light and pollution.

Prop roots become silt roots when they take on the function of flying buttresses. When the tree is older, the bottom of the trunk becomes an upside-down cone shape and may even loose contact with the ground. Prop roots and drop roots improve the stability of the tree by providing a broader base and support in soft mud. Ultrafilters in prop roots exclude salt while extracting water. Above-ground drop roots transport oxygen from the atmosphere to the root system.

Mangrove Pests

A new pest has arrived in Florida that can do some alarming damage to red mangrove leaves in a short space of time. The Myllocerus undatus Marshall is a weevil recently discovered in southeastern Florida from Homestead in the south to Boca Raton in the north. A native of Sri Lanka, these weevils will chew mangrove leaves until there is nothing left to eat. They will attack a variety of both indoor and outdoor plants. We have found that popcorn ceilings attract them and occasionally find one attached to a ceiling. We have found that a wack with a flip-flop is the most effective deterrent at this time.

Besides mangroves, these weevils attack lychee, longan, mamey, areca palms, hibiscus, Australian brush-cherry, cocoplum, tropical almond, crepe-myrtle, akee, citrus, grapefruit, Hong Kong orchid tree, orchid tree, powderpuff, Surinam cherry, orange jasmine, calomondin, red silk-cotton tree, seagrape, Florida trema or neetletree, salt bush or groundsel bush, loquat, Turk's cap, castor bean, earleaf acacia, mother-in-law tongue, black olive, bottlebrush, carrotwood, golden dewdrops, upland cotton, peach, live oak and palms - just about everything that grows in tropical Florida is a meal for Myllocerus undatus Marshall.

Mealy bugs may also attach themselves to mangrove seedlings and the undersides of leaves. Your first line of defense should be physical control... squish the bugs with your fingers. Next, follow up with a cotton swab dipped in rubbing alcohol, dabbing each insect, paying close attention to where the leaf attaches to the stem. Repeat this process until you have eliminated the bugs. Insecticidal soap is an effective alternative to alcohol in their removal.

In Florida and Australia, fungi infestation defoliates and kills red mangroves. Insects such as scales and caterpillars cause defoliation and seedlings are especially vulnerable to the boring beetle.

 

Mangrove propagules will be available after August 1, 2012

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