(aquatic) A plant that is adapted to living either in waterlogged soil or partly or wholly submerged in water. Many hydrophytes absorb water and gases over the whole surface and have no stomata, e.g. the spiked water milfoil (Myriophyllum spicata), which is completely submerged in water. The mechanical and vascular tissue of many hydrophytes is reduced as water is plentiful and supports them. They often have large intercellular air spaces in their stems, roots, and leaves to overcome the difficulty of obtaining gases from the water. Hydrophytes that are partially submerged have floating leaves with stomata through which gases can be exchanged as in land plants. However, to prevent the leaves being flooded with water, the petioles may be very long or shaped like a corkscrew to adjust easily to changes in water level. In the giant water lily (Victoria regia), the enormous leaves have a vertical rim to prevent them from being flooded. Some species, e.g. water crowfoot (Ranunculus aquatilis), have both finely divided submerged leaves and floating leaves with stomata. Hydrophytes are also a class in the * Raunkiaer system of classification and are defined as having their perennating buds under water. The buds may become detached and sink to the bottom (see turion) or may be borne on submerged rhizomes as in water lilies (Nuphar and Nymphaea). Compare mesophyte , xerophyte. See also hydrosere.  |
