Diversity of Plants in Wetlands: The Usumacinta River Watershed, Mexico

Abstract

Various plant communities developed along the Usumacinta River, adjacent streams and lagoons which are all considered part of the wetlands region. The wetlands are characterized for the presence of water, which plays a fundamental role in the development of the soil, and the ecological and structural functions of the system. The vegetation on the borders of the river and streams are known as riverine plant communities, whereas vegetation floating in the bodies of water is known as hydrophytic vegetation \citep{j2006}. Three types of plant species in the wetlands could be distinguished: a) Strictly aquatic: plants that complete their life cycle either totally submerged, partially emerging, or floating on the surface; b) Subaquatic: plants that complete most of their life cycle on the border of the water, in water-saturated soils and can tolerate temporary dry seasons with minor humidity; and c) Drought tolerant: plants which complete most of their life cycle in dry areas, but support being partially submerged during rainy periods. The last category includes trees, bushes, climbers, and some palms \citep{2015}.The aquatic and border vegetation are physically and biologically connected and are of ecological importance, providing complex habitats and resources for a high variety of other aquatic organisms \citep{j2006}. The knowledge of the aquatic and subaquatic vegetation in Mexico is fragmentary. In particular for the Usumacinta River (the most important river of Mexico) where watershed has been only partially studied. In this study, we revised and created the knowledge available on the plant communities, the riparian and aquatic plant species along the Usumacinta River watershed, and supplemented this knowledge with data collected in the study area. The data of floristic inventory of the Usumacinta river watershed was integrated with data provided by the National System of Information on Biodiversity of the National Commission for the Knowledge and Use of the Biodiversity (SNIB-CONABIO), literature, herbaria samples of UAC, ENCB, UJAT, Ecosur-SCLC and MEXU, and field data.We registered 212 families and 3,501 species; the families with most species were those of legumes (342), followed by orchids (295), the composite family (214), and grasses (195) \citep{delgado2018}. Such numbers of plant species is a good indication of the great diversity and floristic richness of aquatic and border plants in the Usumacinta River watershed. We registered 36 families and 148 aquatic and subaquatic plant species, numbers which confirm the importance of the Usumacinta watershed for these species groups.The borders of the Usumacinta River are threatened by human activity. The villages’ are planting ornamental and fruit trees, both native as introduced species. However, it is still possible to find original plant communities either in the lagoons, or along the Usumacinta river; for example, shrublands of muco (Dalbergia brownei or D. glabra) \citep{santiago2005}. The most common tree species registered are typical of riverine forest communities, such as: Bucida buceras (pucte), Inga vera (jinicuil), Haematoxylum campechianum (tinto), Pithecellobium lanceolatum (tucuy) and Salix humboldtiana (sauce), all of which are still present in border-forested fragments along the Usumacinta, San Pedro and Palisade rivers \citep{e1963} \cite{santiago2005}. The border vegetation near the coast is dominated by mangroves, such as Rhizophora mangle (red mangle), associated with Laguncularia racemosa (white mangle), Avicennia germinans (mangle prieto) and Conocarpus erectus (botoncillo) \cite{j2006}.We registered five species which had value and/or use: Annona glabra (anona) which is edible, Crescentia cujete (jicaro) which is ornamental, Guatteria anomala (palo de zope) which is used as food of turtles and parakeets, Sagittaria lancifolia (tule), and Vallisneria americana (sargazo) which is also known to be in the diet of turtles. This work highlights the importance of the riverine and aquatic vegetation for human communities, besides the service of food, nesting sites, refuge and rest for the regional fauna.This diversity of plants is integrated in plant communities which stabilizes the silt, oxygenates the water, provides refuge and material for nest sites, are habitats for different species of fauna, and provides multiple ecosystem services which depend partly on the population that lives in the region \citep{a2010}. The villagers depend on the hydrological functions because fishing is an important source of economic income, and a local food source. Many of people that live in the watershed recognize the importance of the plants as a source of food for the aquatic fauna. As such, the management and conservation of the wetlands is of great importance.Diversidad de Plantas en Humedales de la Cuenca del rio Usumacinta, Mexico