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Aquatic Plants
Aquatic plants show several adaptations to the life in water. Most of them lack a waxy surface on their leaves so the surface remains wet and the exchange of gases with the water can occur. Aquatic plants generally have elongated stems and softer tissues that terrestrial plants.
Aquatic plants include species of the common group of flowering plants (angiosperms) as well as some fern species.
Recuadro: Plants are derived from an aquatic ancestor. Those plants that we now call aquatic plants are probably derived from terrestrial ancestors that evolved to be suitable to aquatic environments.
The aquatic plants vary in the degree they are related to the water. They can be classified in at least six different associations with water, from those who resist flooded areas to the ones that live submerged under the water.
- Wetland plants: these are the plants that you see living in flooded areas. They do not show particular adaptation to the life in water. Some species in these category are the Palo Verde tree (Parkinsonia aculeata, which gives name to the Palo Verde National Park) the michigüiste tree (Pithecellobium lanceolatum), and the Dormilona shrub (Mimosa pigras).
- Emergent plants: These plants start their life in the water, but after they have grown enough to flower they are emergent, which means that they are above the water. That is the case of the cattail (Typha dominguensis), an herb that became dominant in the Palo Verde wetlands and caused a management program to keep the water mirror visible for the migrating birds to land. Other emergent plants are the sedge (Cyperus giganteus, C. articulatus, C. digitatus), the “Platanillo” with purple flowers (Thalia geniculata), Canna glauca, Caperonia palustris.
- Amphibious plants: as the name says it, these plants can live in both earth and water. Therefore, they can be found in shallow waters (even in temporary ponds on hiking trails), where the level of water fluctuates over time. They produce flowers only during their terrestrial stage. Examples of these amphibious plants include the pepperwort fern and the water clover (trébol de agua, Marsilea deflexa and M. polycarpa), Mayaca fluviatilis and Myriophyllum aquaticum.
- Floating plants that are rooted in the ground: these plants have the stem or leaves above the water surface, but their roots go down to the ground, so the plants are “anchored”. The waterlily (flor de loto, Nymphaea sp), Eichornia diversifolia, Ludwigia sedoides, the Bacopa (Bacopa repens).
- Floating Plants: these plants truly float free on the water surface. Includes the water-hyacinth (Lirio de agua, Eichornia crassipes) with a beautiful white flower, the duckweed (Lemna aequinoctialis), the mosquito fern (Azolla microphylla), and the water spangles (ferns, Salvinia auriculata), all the last three small but surprisingly beautiful if watched closely. Azolla is associated with bacteria that fix nitrogen. The bacteria live inside little hollows in the leaves. Therefore, these plants enrich the environment for the other plants and some farmers use them in their crops.
- Submerged plants: these plants are often rooted in the ground, and live submerged in the water. Some of them are water-pollinated, but some others have emergent flowers to be pollinated by insects or by wind. Examples of this plant include the bladderwort (atrapamoscas, Utricularia foliosa, U. gibba, U. hydrocarpa), the naiad (Najas arguta and N. guadalupensis), and the coontail (candelabro de agua, Ceratophyllum muricatum, C. demersum).
Sources: Crow, G. 2002. Plantas acuáticas del Parque Nacional Palo Verde y el valle del río Tempisque. INBio, Heredia, Costa Rica. 300 p.
Simpson, M. 2006. Plant systematics. Elsevier. 590 p.
