Self-Cloning Seagrass Breaks World Record for Largest Plant

australian seagrass meadow is 70 square miles

By Jonny Lupsha, Wondrium Staff Writer

A seagrass meadow in Australia has been cloning itself for 4,500 years. Scientists have confirmed through DNA tests that the enormous meadow is a single organism. Seagrass is adaptable and resilient.

Field of seagrass underwater
Seventy species of seagrass are distributed in four different families of flowering plants and grow entirely underwater in sandy or muddy bottoms of shallow coastal waters. Photo by think4photop / Shutterstock

A meadow of seagrass that measures 70 square miles is the subject of a recent study funded by Australia’s National Environmental Science Program. The seagrass is approximately 4,500 years old and is the largest known plant on Earth. Scientists were able to confirm that the entire meadow is the same organism by testing its DNA in various locations.

Many species of plant life like seagrass are the result of plants that evolved from shallow waters to land before returning to sea. In her video series Plant Science: An Introduction to Botany, Dr. Catherine Kleier, Associate Dean of Faculty in the College of Agriculture, Food, and Environmental Sciences at California Polytechnic State University, explains seagrasses like the one in Australia.

Adaptable Grass

“Some 70 species of seagrass are distributed in four different families of flowering plants,” Dr. Kleier said. “Most likely, these groups diverged from a single, monocot flowering plant around 100 million years ago. Despite being in different families with growth forms that vary from grass-like to very leafy, all seagrasses grow in similar habitats.”

Those habitats are sandy or muddy bottoms of shallow coastal waters. Since they all grow in the same habitat, all seagrasses deal with the same environmental stress factors. Nutrient-poor sediment, low oxygen levels, and even low light levels—which are caused by the sediment kicked around in the habitat—all present challenges for life in the shallows.

How do seagrasses thrive in such a troubled environment? According to Dr. Kleier, in order to absorb more light, seagrasses put their chloroplasts—where photosynthesis happens—on their outermost layer. On the subject of photosynthesis, one of the waste products of photosynthesis is oxygen. Seagrasses are able to release the waste product of oxygen directly back into their own tissues, which disseminate the oxygen into their stems.

As for nutrients, seagrasses not only absorb minerals from ocean water, but they also have bacteria living in their roots that break down nitrogen into a usable form.

So Much for Wining and Dining

Although the enormous meadow of seagrass in Australia is cloning itself, seagrasses usually reproduce the old-fashioned way: pollination. Since bees aren’t there to help, nor does pollen swim, this leaves three options for pollen to travel from the male plant to the female.

“First, the pollen can float to the surface of the water when tides are at their lowest and drop pollen from there onto, hopefully, the female plants below,” Dr. Kleier said. “Secondly, pollen can conglomerate on the top of the substrate—be it sand or mud—and form a collective tower, which can reach a meter in length. A third type of pollen dispersal—and this is the same mechanism used by many marine mammals—involves broadcasting sperm into the ocean water and, again, hoping for the best.

“This is also called hydrophilous pollination.”

After a female plant has been pollinated, it bears fruit, which need to be dispersed. In the case of seagrasses, this fruit is usually dispersed by ocean currents. However, according to Dr. Kleier, none of the seeds actually float, so when the fruit is eaten or has settled somewhere on the sea floor, the seed attempt germination wherever it lands. It could take hours or it could take years.

“It’s hard to have rules in botany.”

Edited by Angela Shoemaker, Wondrium Daily