Most plants hate saltwater. Pour saltwater on your houseplants and, a little while later, you’ll have some wilty plants. But mangroves can grow—and thrive—in saltwater.
You may have seen mangroves if you’ve been to the Florida Everglades or gone to an island in the Caribbean. Mangroves are trees that live in tropical, coastal zones and have special adaptations for life in saltwater. One of these adaptations is in how they reproduce: mangroves don’t make seeds. Instead, they make living, buoyant embryos called propagules (prop-a-gyule).
Mangrove propagules come in different shapes and sizes. Each species has its own unique propagule.
Normally, trees reproduce with seeds. You’ve probably seen the whirlybirds of maples and acorns of oaks. These seeds can go dormant. They are basically “asleep” or hibernate until something—water, temperature, or physical damage—wakes them up, allowing them to start growing months or years after they are produced.
Propagules, on the other hand, don’t have that luxury—they fall off their parent tree, ready to start rooting and growing a new tree. Nature has provided an amazing way for the mangrove seeds to move away from the parent tree: they float.
As the propagules float through the water, they shed their outermost layer and immediately start growing roots. The clock starts ticking as soon the propagules fall—if they don’t find a suitable place to start growing within a certain amount of time, they die. If a mangrove propagule ends its journey at a location that’s suitable for growth, the already-rooting propagule will send up its first set of leaves—cotyledons.
Ocean currents can take propagules thousands of miles away from where they started. A mangrove’s parent tree might be around the corner or around the continent.
Dr. Emily Dangremond is a postdoctoral researcher at the Smithsonian Environmental Research Center and a visiting scientist at the Chicago Botanic Garden. She is currently studying the ecological and evolutionary consequences of mangroves responding to climate change at their northernmost limit in Florida.
Students in the Chicago Botanic Garden and Northwestern University Program in Plant Biology and Conservation were given a challenge: Write a short, clear explanation of a scientific concept that can be easily understood by non-scientists. This post is part of their series.
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