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Duckweed or Suckweed? Tiny Plants Turn Out to be Interesting!

by Julie Everett

Growing up, I had a forsythia bush in my backyard. For some reason, each spring my sister and I would always eat the flowers from it while we were playing outside. I’m not sure why we kept doing that, and I’m not sure if the flowers are even safe to eat, but we both turned out fine (and with an appetite to consume science in a more appropriate way).

My younger self playing with a juvenile red spotted salamander, Notophthalmus viridescens, at camp.

Back then, plants were something for me to use and play with, similar to my toys inside, but provided by nature. I remember gathering leaves and mud to make ‘salad with dressing’, complete with a flower as garnish on top. We would leave our feast to rot in buckets and sand pails until they were so stinky that there was no choice but to throw the whole creation away, buckets and all. I remember yanking out the dried stalks of daylilies and using them as torches when we were playing pretend. Stripping the leaflets from a fern branch as a bouquet to present as a gift to each other. Eating the flowers off of the forsythia bush.

I also remember pulling up patches of moss at my grandad’s hunting camp to search for those spunky little orange salamanders. If we found three of them, my mom would let us take them home for the summer and feed them worms from the backyard (three because she didn’t want them to get lonely). At this point in my life, plants weren’t interesting to me in the way that the salamanders that I caught were, which I would let crawl across my hand and up my arms. I could feed worms to the salamanders and watch as the salamanders would fight over the same worm, the winner pulling the worm out of the mouth of the other salamander after it had already been half-swallowed. As I became more interested in biology and ecology, I continued ignoring plants in favor of more exciting animals, especially amphibians (my favorites).

Three species of duckweed commonly found in western Pennsylvania: Lemna minor, Spirodela polyrhiza , Wolffia brasiliensis.

That all changed about a year ago when I joined a research lab at my university. This lab works with duckweed, which are plants with tiny leaflets that float in slow-moving, freshwater habitats. Over the summer my lab mates and I have done a lot of field sampling; going out to parks and state game lands in search of more duckweed samples to add to the lab’s collection. Throughout this process, I’ve found a fascination with these little plants in a way I’ve never had with plants before.

Duckweed reproduces clonally, meaning that each leaflet--or frond as we call them scientifically--creates a clone of itself that will eventually detach and become its own separate plant. Each daughter frond is an exact genetic copy of its mother, similar to how identical twins share identical genetic material. Interestingly though, even though these little guys are clones of each other, there’s huge diversity in how their genotypes are expressed, based on the environment they are in.

This can happen with humans too. Think about identical twins. Imagine that one of them only eats junk food and pasta, always skips breakfast, and never exercises. The other is an athlete, eats high-protein diets, and goes to the gym regularly. Even though these two individuals share the same exact DNA, they will end up looking very different from each other. This phenomenon is called phenotypic plasticity, which means that there is flexibility in how the genes of an individual are expressed, based on their surrounding environment. You can read more about phenotypic plasticity here and here.

Duckweed species Lemna minor with identical genotypes in identical containers at the start of a field experiment (left) and then a month later (right).

I’ve seen plasticity in the duckweed that we find in the field. Most often, we find smaller duckweed in the field, and when we bring them back to grow in lab where there is plenty of light and mineral nutrients available for them, their daughter fronds grow bigger and greener. However, occasionally the opposite is true, where we find very large fronds in the field and when we bring them back to the lab, their daughters grow smaller. I’ve now spent so much time with duckweed, I can tell the condition of the duckweeds’ environment just by the way the plants look. These changes in the duckweed are plastic though, and once you take a duckweed plant out of the environment it is currently in and put it in a different one, the fronds it produces are will change in appearance from the mother frond to reflect their new environment.

In this photo above, it looks like the picture taken a month later is zoomed out, but the water level difference between the two images is only about one or two centimeters. The difference in size of the duckweed fronds could be an example of plastic effects caused by depleted nutrient levels and increased crowding over the course of the month.

A baby snapping turtle, Chelydra serpentina, found in a dense patch of the duckweed species Lemna minor.

Thanks to my experiences this past year, now when I’m out in the woods, I’m not only on the lookout for my little salamander buddies that hide under logs, rocks, and leaflitter, but for my duckweeds as well in ponds, lakes, and slower-moving streams. It turns out that finding duckweed is just as exciting as turning over a log and finding a salamander! Though, perhaps the most exciting hike is when you find both plants and critters.

Salamander egg mass found among Lemna minor. Some developed larvae are visible.

Julie is currently a senior Ecology and Evolution student at the University of Pittsburgh. Though she has found a new love for plants, she still finds amphibians and reptiles the most interesting!

Photo Credits: CC BY-SA 3.0, (top photo); Julie Everett (remaining photos)


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