What's Blooming August 19: The Red Mangrove

Rhizophora mangle (Rhizophoraceae)
Red mangrove (Red mangrove family)
Origin: Tropical estuaries around the world

This week’s featured plant is an essential player in Florida’s coastal ecosystem. Not only do red mangroves provide habitat for dozens of species of birds, fish, and crustaceans, including crabs that live nowhere else, but they help protect our coasts from erosion. This is especially important in hurricane season. During the rest of the year, mangroves help to minimize ripples and waves, creating still-water pools that provide protection for smaller plants and animals which could not weather the rough seas otherwise. Mangroves do this is through their prop roots, which resemble a tangle of small arms reaching down into the water. These roots hold the stem of the mangroves up out of the water, and act like a huge filtration system. These trees are capable of reaching many dozens of meters tall, but most people who live on the water wish to keep them more like hedges, not to block their water view. Owners need a special permit to trim mangroves, and it is illegal here in Sarasota to cut them any shorter than six feet from the substrate. In reality, there are few “looks” more Floridian than the sun setting through a tangle of red mangrove roots while a heron fishes for his dinner.

Perhaps one of the coolest things about Rhizophora mangle is the way the seeds germinate directly on the mother plant (termed vivipary). Most plants bloom, set seed, and then release the seed to be carried away and germinated in another place where conditions are right. This is even true for most coastal plants which use water as a dispersal mechanism (think coconuts.) The seeds of the red mangrove, however, germinate and begin to grow directly on the parent plant. These germinated seeds, called “propagules” look like string beans and can be seen in abundance hanging off of the mangrove branches. When they are ready, they are released, buoyantly floating off to find a beach or sandbar somewhere to sink into and grow roots and leaves. They are already green and actively photosynthesizing before they even drop into the water.

At Marie Selby Botanical Gardens, we have all three mangroves native to Florida (red, black, white) growing both bayside and on the bayou. The red mangroves are blooming right now, many showcasing propagules along their branches.

Text by David Troxell