Morpho-anatomical adaptations of Centella asiatica (Apiaceae) in different coastal sand microenvironments of Restinga and in an urbanized area

Restinga, a coastal sand environment, has low availability of organic matter, natural soil acidity, fast water drainage, high solar incidence, high salinity, strong winds and coastal flooding, which may require specific plant traits. This study analyzed the morphoanatomy of C. asiatica occurring in different microenvironments of Restinga and in an urbanized area to identify adaptive characteristics to each respective environment. Samples of roots, stolons, and leaves from sunny waterlogged dune slack, sunny wet dune slack, shaded wet dune slack, and shaded dry dune slack, and in an urbanized area were collected. Twenty three variables were measured, besides general histochemistry and soil characteristics. The one-way variance analysis (ANOVA) and principal component analysis (PCA) indicated that C. asiatica plants enhance different traits depending on the environment. Plants in shady microenvironments have greater petiole length, leaf area, fresh mass and leaf dryness compared to those occurring in sunny microenvironments. C. asiatica leaves are amphistomatic and in sunny microenvironments the chlorenchyma is more developed and has greater stomatal density on the abaxial surface. In urbanized areas, plants showed increased leaf area and fresh mass, and petiole thickening, and decreased leaf blade thickening. These traits may be related to the clay soil, which has greater water retention, and also to the shaded environment. Such adaptations allow the C. asiatica plants to maximize energy gain under different environmental conditions. Secretory canals were identified in all analyzed organs, which secreted acidic and neutral polysaccharides. We recorded for the first time the presence of hydathodes on the serrated margins of C. asiatica leaf blades. This study expands the knowledge on species occurring in coastal sand environments and the modifications presented to survive in distinct microenvironments of Restinga.