Numerous lines of evidence indicate that aquatic angiosperms originated on the land. Adaptation and specialization to the aquatic habitat have been achieved by only a few angiosperms (< 1%) and pteridophytes (< 2%). Consequently, the richness of plant species in aquatic and wetland habitats is relatively low compared with most terrestrial communities (Richardson and Vymazal, 2001). Most are rooted, but a few species float freely in the water (Wetzel, 2001).
Tiner (1999) pointed out that plants growing in wetlands and water are technically called hydrophytes. However, today’s usage of the term hydrophyte is different than its original use. In the 1800s and early 1900s, it was used to define aquatic plants that were plants growing in water (Schouw, 1822, as reported in Warming, 1909) or plants with perennating buds beneath the water (Raunikaer, 1905, 1934). Warming and Raunkiaer were among the earliest of the plant ecologists to use the term hydrophyte. Hydrophytes were distinguished from helophytes, which included various wetland plants depending on whose definition was used (Tiner, 1999). Raunkier’s life-form were based on a plant’s adaptation to the critical season (e.g., winter) mainly the degrees of protection possessed by the dormant buds (Smith, 1913). According to this system, hydrophytes (plants with perennating rhizomes or winter buds) and helophytes (plants with buds at the bottom of the water or in the underlying soil) were the two types of cryptophytes (plants with dormant parts below ground), while other wetland plants were included in other life-forms, such as phanerophytes (trees and shrubs) (Smith, 1913). Raunkiaer’s helophytes did not include all typical marsh plants. Tinner (1999) reported that Warming (1909) was probably the first ecologist to arrange plant communities according to the degree of soil wetness. He recognized aquatic plants (water-plants) that spend their entire life submerged or with leaves floating at the surface and terrestrial plants that are mostly exposed to air, including marsh plants. Vegetation was then separated into numerous “oecological classes” based principally on soil properties. The first of the groupings was for soil that was very wet: 1) hydrophytes (formation in water) and 2) helophytes (formation in marsh). Clements (1920) might have been the first ecologist to expand definition of hydrophytes in include helophytes as a type of hydrophyte.
KeywordsPhosphorus Sulphide Convection Mercury Manifold
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