section_path: Pollination/Abiotic pollination
section_name: Abiotic pollination
paragraph_text: Abiotic pollination
  
  Flowers that use abiotic, or non-living, vectors use the wind or, much less commonly, water, to move pollen from one flower to the next. In wind-dispersed (anemophilous) species, the tiny pollen grains are carried, sometimes many thousands of kilometers, by the wind to other flowers. Common examples include the grasses, birch trees, along with many other species in the order Fagales, ragweeds, and many sedges. They do not need to attract pollinators and therefore tend not to grow large, showy, or colorful flowers, and do not have nectaries, nor a noticeable scent. Because of this, plants typically have many thousands of tiny flowers which have comparatively large, feathery stigmas; to increase the chance of pollen being received. Whereas the pollen of entomophilous flowers is usually large, sticky, and rich in protein (to act as a "reward" for pollinators), anemophilous flower pollen is typically small-grained, very light, smooth, and of little nutritional value to insects. In order for the wind to effectively pick up and transport the pollen, the flowers typically have anthers loosely attached to the end of long thin filaments, or pollen forms around a catkin which moves in the wind. Rarer forms of this involve individual flowers being moveable by the wind (pendulous), or even less commonly; the anthers exploding to release the pollen into the wind.
  
  Pollination through water (hydrophily) is a much rarer method, occurring in only around 2% of abiotically pollinated flowers. Common examples of this include Calitriche autumnalis, Vallisneria spiralis and some sea-grasses. One characteristic which most species in this group share is a lack of an exine, or protective layer, around the pollen grain. Paul Knuth identified two types of hydrophilous pollination in 1906 and Ernst Schwarzenbach added a third in 1944. Knuth named his two groups 'Hyphydrogamy' and the more common 'Ephydrogamy'. In hyphydrogamy pollination occurs below the surface of the water and so the pollen grains are typically negatively buoyant. For marine plants that exhibit this method, the stigmas are usually stiff, while freshwater species have small and feathery stigmas. In ephydrogamy pollination occurs on the surface of the water and so the pollen has a low density to enable floating, though many also use rafts, and are hydrophobic. Marine flowers have floating thread-like stigmas and may have adaptations for the tide, while freshwater species create indentations in the water. The third category, set out by Schwarzenbach, is those flowers which transport pollen above the water through conveyance. This ranges from floating plants, (Lemnoideae), to staminate flowers (Vallisneria). Most species in this group have dry, spherical pollen which sometimes forms into larger masses, and female flowers which form depressions in the water; the method of transport varies.