Early this year I was able in observe tropical aquatic plants in their home environment and notice what the natural conditions are like. A big surprise to me was the environment I found some of these plants. Sure, the floating plants and marginal plants were on the side of rivers and ponds but there were some notable exceptions. The location was Costa Rica, home of incredible biodiversity: whether it be insects, plants, birds, or mammals, Costa Rica is right at the top with one of the highest number of species per area. But as for the aquatic plants, I really didn’t notice that many species because I was rather busy looking for birds.
The first surprise was an old familiar plant that I kept in one of my first tanks: this was Heteranthera reniformis. Looking nothing like its feathery cousin, the water stargrass (H. zosterifolia), this plant looks like a miniature water lily with hard, small, and round heart-shaped leaves. It grows in water-logged soil or very shallow water (as in long-term puddles) and also along the edges of streams. I found it growing on the sandy shallows of a stream that passes by the lava flow of the Arenal volcano. The remarkable thing wasn’t the plant itself but where it was growing. Arenal is an active volcano and the water temperature reaches 42C in some of the pools. With the exception of algae and this plant the stream was devoid of vegetation.
Beside the road, high in the Cordillera de Tilarán, I made two interesting discoveries. First, anywhere the soil was damp I found a type of pennywort (Hydrocotyle sp.). While we are used to seeing the aquatic species, this was most definitely a terrestrial form for the areas they frequented were not likely to flood. In fact under heavy rain the small ditches where they were would allow the water to flow very fast and carry a lot of sediment. The second discovery was an orchid, Sobralia powellii that grew profusely beside the road. I had never thought of orchids as ditch flowers!
On the Caribbean side I saw first hand the challenges that aquatic plants face in a forest environment. The frequent showers mean greatly fluctuating water levels. The forest canopy allows little light to reach the water and the fallen leaves stain the water dark, so the little light doesn’t penetrate far. I had seen black water streams before, but never ones so dark. I expected tea-colored water but in some places the water was as dark as Coke.
In the shallow streams the soil was clay with a thick layer of decomposing leaves, ideal habitat for Apistogramma and banjo catfish. The water here was very clear. In this setting I found, of all things, a water lily (Nymphaea sp.) with white flower buds.
In the larger streams the water was very muddy and I didn’t expect to see any submerged plants. Yet I saw pieces of what looked like Egeria densa close to shore. The shores themselves were mostly bordered by water hyacinth (Eichhornia crassipes) with a small species of Salvinia growing in the sheltered water between the plants. Flowers were not plentiful at the time and there were mats of these plants floating down the river. The largest mat was over three meters wide and contained grasses and a flowering creeper growing on top of the water hyacinth. Talk about biodiversity!
The final surprise came as a large patch of papyrus growing on a stretch of the river. The common papyrus (Cyperus papyrus) is an African plant, so what were these plants doing in Costa Rica? The family Cyperaceae has a worldwide distribution, so it is possible that these were of a Central American species. Another possibility, perish the thought, is that the plants are descendants of introduced ornamentals planted in someone’s garden. At any rate, they looked very out of place.
That’s pretty much all that I saw of aquatic plants. Considering that they were not the main focus of my trip I am very pleased to have seen them in a natural setting. I also learned to expect the unexpected.
Riehl, Rüdiger, and Baensch, Hans A. (1986). Aquarium Atlas. Melle, Germany: MERGUS-Verlag.
Riehl, Rüdiger, and Baensch, Hans A. (1993). Aquarium Atlas Volume 2. Melle, Germany: MERGUS-Verlag. ?