Water pollination (hydrophily)

Water-pollinated plants are aquatic and pollen is released into the water. Water currents therefore act as a pollen vector in a similar way to wind currents. Their flowers tend to be small and inconspicuous with lots of pollen grains and large, feathery stigmas to catch the pollen. However, this is relatively uncommon (only 2% of pollination is Hydrophily) and most aquatic plants are insect-pollinated, with flowers that emerge into the air. Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface - the most common adaptation is aerenchyma, but floating leaves and finely dissected leaves are also common.[1][2][3] Aquatic plants can only grow in water or in soil that is permanently saturated with water. They are therefore a common component of wetlands.[4] The principal factor controlling the distribution of aquatic plants is the depth and duration of flooding. However, other factors may also control their distribution and abundance, including nutrients, disturbance from waves, grazing, and salinity.[5] Aquatic vascular plants have originated on multiple occasions in different plant families;[6][7] they can be ferns or angiosperms (including both monocots and dicots). Seaweeds are not vascular plants; rather they are multicellular marine algae, and therefore are not typically included among aquatic plants. A few aquatic plants are able to survive in brackish, saline, and salt water.[8] Examples are found in genera such as Thalassia and Zostera. Although most aqua ic plants can reproduce by flowering and setting seed, many also have extensive asexual reproduction by means of rhizomes, turions, and fragments in general.[9] One of the largest aquatic plants in the world is the Amazon water lily; one of the smallest is the minute duckweed. Many small aquatic animals use plants like duckweed for a home, or for protection from predators. But areas with more vegetation are likely to have more predators. Some other familiar examples of aquatic plants might include floating heart, water lily, lotus and water hyacinth. Some aquatic plants are used by humans as a food source. Examples include wild rice (Zizania), water caltrop (Trapa natans), Chinese water chestnut (Eleocharis dulcis), Indian lotus (Nelumbo nucifera), water spinach (Ipomoea aquatica) and watercress (Rorippa nasturtium-aquaticum) When soil is flooded, hypoxia develops, as soil microorganisms consume oxygen faster than diffusion occurs. The presence of hypoxic soils is one of the defining characteristics of wetlands. Many wetland plants possess aerenchyma, and in some, such as water-lillies, there is mass flow of atmospheric air through leaves and rhizomes.[4] There are many other chemical consequences of hypoxia. For example, nitrification is inhibited as low oxygen occurs and toxic compounds are formed, as anaerobic bacteria use nitrate, manganese, and sulfate as alternative electron acceptors.[5] The reduction-oxidation potential of the rhizhosphere decreases and metal ions such as iron and manganese precipitate. In general, low oxygen stimulates trees and plants to produce ethylene.[6] Ethylene slows down primary and adventitious root elongation and formation.