Anemophily orwind pollination is a form ofpollination wherebypollen is distributed bywind.[1] Almost allgymnosperms are anemophilous, as are many plants in the orderPoales, includinggrasses,sedges, andrushes.[1] Other common anemophilous plants areoaks,pecans,pistachios,sweet chestnuts,alders,hops, and members of the familyJuglandaceae (hickory or walnut family).[2] Approximately 12% of plants across the globe are pollinated by anemophily, includingcereal crops likerice andcorn and other prominent crop plants likewheat,rye,barley, andoats.[3] In addition, manypines,spruces, andfirs are wind-pollinated.[2]
Features of the wind-pollination syndrome include a lack of scent production, a lack of showy floral parts (resulting in small, inconspicuous flowers), reduced production ofnectar, and the production of enormous numbers of pollen grains.[4] This distinguishes them fromentomophilous andzoophilous species (whose pollen is spread byinsects andvertebrates respectively).[citation needed]
Anemophilouspollen grains are smooth, light, and non-sticky, so that they can be transported by air currents.[5] Wind-pollinating plants have no predisposition to attract pollinating organisms.[2] They freely expel a myriad of these pollen grains, and only a small percentage of them ends up captured by the female floral structures on wind-pollinated plants.[3] They are typically 20–60 micrometres (0.0008–0.0024 in) in diameter, although the pollen grains ofPinus species can be much larger and much less dense.[1] Anemophilous plants possess lengthy, well-exposedstamens to catch and distribute pollen.[2] These stamens are exposed to wind currents and also have large, featherystigma to easily trap airborne pollen grains.[5] Pollen from anemophilous plants tends to be smaller and lighter than pollen from entomophilous ones, with very low nutritional value to insects due to their low protein content.[2] However, insects sometimes gather pollen from staminate anemophilous flowers at times when higher-protein pollens from entomophilous flowers are scarce. Anemophilous pollens may also be inadvertently captured bybees'electrostatic field. This may explain why, though bees are not observed to visitragweed flowers, itspollen is often found inhoney made during the ragweed floral bloom. Other flowers that are generally anemophilous are observed to be actively worked by bees, with solitary bees often visitinggrass flowers, and the largerhoneybees andbumblebees frequently gathering pollen fromcorn tassels and other grains.[citation needed]
Anemophily is anadaptation that helps to separate the male and female reproductive systems of a single plant, reducing the effects ofinbreeding.[6] It often accompaniesdioecy – the presence of male and female reproductive structures on separate plants.[citation needed] Anemophily is adaptively beneficial because it promotesoutcrossing and thus the avoidance ofinbreeding depression that can occur due to the expression of recessive deleteriousmutations in inbred progeny plants.[7]
Almost all pollens that areallergens are from anemophilous species.[8] People allergic to the pollen produced by anemophilous plants often have symptoms of hay fever.[2] Grasses (Poaceae) are the most important producers of aeroallergens in most temperate regions, with lowland or meadow species producing more pollen than upland ormoorland species.[8] In Morocco, it was found that asthma caused by pollen from Poaceae accounted for 10% of the clinical respiratory diseases that patients faced.[9] The nature of how species of Poaceae grasses flower results in an increase in the time that the allergenic pollen circulates through the air, which is not favorable to people who are hypersensitive to it.[9]
Media related toWind pollination at Wikimedia Commons