Hydrophily
Hydrophily is a fairly uncommon form of pollination whereby pollen is distributed by the flow of waters, particularly in rivers and streams. Hydrophilous species fall into two categories: (i) Those that distribute their pollen to the surface of water. e.g. Vallisneria's male flower or pollen grain are released on the surface of water, which are passively carried away by water currents; some of them eventually reach the female flower (ii) Those that distribute it beneath the surface. e.g. seagrasses in which female flower remain submerged in water and pollen grains are released inside the water.
Surface pollination
Surface pollination is more frequent,[1] and appears to be a transitional phase between wind pollination and true hydrophily. In these the pollen floats on the surface and reaches the stigmas of the female flowers as in Hydrilla, Callitriche, Ruppia, Zostera, Elodea. In Vallisneria the male flowers become detached and float on the surface of the water; the anthers are thus brought in contact with the stigmas of the female flowers.[1] Surface hydrophily has been observed in several species of Potamogeton as well as some marine species.[2]
Submerged pollination
Species exhibiting true submerged hydrophily include Najas, where the pollen grains are heavier than water, and sinking down are caught by the stigmas of the extremely simple female flowers,[1] Posidonia australis or Zostera marina[3] and Hydrilla.
Evolution
Hydrophily is unique to obligate submersed aquatic angiosperms with sexually reproductive parts completely submerged below the water surface. Hydrophily is the adaptive evolution of completely submersed angiosperms to aquatic habitats. True hydrophily occurs in 18 submersed angiosperm genera, which is associated with an unusually high incidence of unisexual flowers.[4]
References
- Chisholm 1911, p. 3
- Zhang, Xiao-lin; Gituru, Robert W.; Yang, Chun-feng; Guo, You-hao (2010). "Exposure to water increased pollen longevity of pondweed (Potamogeton spp.) indicates different mechanisms ensuring pollination success of angiosperms in aquatic habitat". Evolutionary Ecology. 24 (4): 939–953. doi:10.1007/s10682-010-9351-z. ISSN 0269-7653. S2CID 1512192.
- Cox 1988, pp. 261–279.
- Du, Z.-Y., Wang, Q.-F. (19 December 2014). "Correlations of Life Form, Pollination Mode and Sexual System in Aquatic Angiosperms". PLOS ONE. Public Library of Science. 9 (12): e115653. doi:10.1371/journal.pone.0115653. ISSN 1932-6203. PMC 4272260. PMID 25525810.
Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Sources
- Cox, P.A. (1988). "Hydrophilous pollination". Annual Review of Ecology and Systematics. 19 (1): 261–279. doi:10.1146/annurev.es.19.110188.001401.
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Pollination". Encyclopædia Britannica. Vol. 22 (11th ed.). Cambridge University Press. pp. 2–5.