Rhizoid

Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi and sponges. Rhizoids may be unicellular or multicellular.^[1]

Evolutionary development

Plants originated in aquatic environments and gradually migrated to land during their long course of evolution. In water or near it, plants could absorb water from their surroundings, with no need for any special absorbing organ or tissue. Additionally, in the primitive states of plant development, tissue differentiation and division of labor were minimal, thus specialized water-absorbing tissue was not required. The development of specialized tissues to absorb water efficiently and anchor the plant body to the ground enabled the spread of plants onto land.^[2]

Description

Rhizoids absorb water mainly by capillary action in which water moves up between threads of rhizoids; this is in contrast to roots in which water moves up through a single root. However, some species of bryophytes do have the ability to take up water inside their rhizoids.^[2]

Land plants

In land plants, rhizoids are trichomes that anchor the plant to the ground. In the liverworts, they are absent or unicellular, but they are multicellular in mosses. In vascular plants, they are often called root hairs and may be unicellular or multicellular.

Algae

In certain algae, there is an extensive rhizoidal system that allows the alga to anchor itself to a sandy substrate from which it can absorb nutrients.^[3] Microscopic free-floating species, however, do not have rhizoids at all.^[4]

Fungi

In fungi, rhizoids are small branching hyphae that grow downwards from the stolons and anchor the fungus to the substrate, where they release digestive enzymes and absorb digested organic material.^{[citation needed]}

Sponges

Rhizoid-like structures are also present in some species of sponge, where they are used to anchor the sponge into the ground. One notable example of this structure is in the lyre sponge (Chondrocladia lyra), which feeds carnivorously via "branches" that grow vertically off of stolons located on top of the rhizoid.^[5]

References

^ Fletcher, Robert L. (1987). Seaweeds of the British Isles, Volume 3 Fucophyceae (Phaeophyceae). British Museum (Natural History). ISBN 0-565-00992-3.
^ ^a ^b Jones VA, Dolan L (July 2012). "The evolution of root hairs and rhizoids". Annals of Botany. 110 (2): 205–212. doi:10.1093/aob/mcs136. PMC 3394659. PMID 22730024.
^ Demes KW, Littler MM, Littler DS (2010). "Comparative phosphate acquisition in giant-celled rhizophytic algae (Bryopsidales, Chlorophyta): Fleshy vs. calcified forms". Aquatic Botany. 92 (2): 157–160. doi:10.1016/j.aquabot.2009.10.012.
^ Smith GM (1955). Cryptogamic Botany, Volume 1 Algae and Fungi. McGraw-Hill Book Company Inc.
^ Lee, Welton L.; Reiswig, Henry M.; Austin, William C.; Lundsten, Lonny (2012). "An extraordinary new carnivorous sponge, Chondrocladia lyra, in the new subgenus Symmetrocladia (Demospongiae, Cladorhizidae), from off of northern California, USA". Invertebrate Biology. 131 (4): 259–284. doi:10.1111/ivb.12001. ISSN 1077-8306.

External links

"Rhizoids" . The New Student's Reference Work . 1914.
"Rhizoids" . New International Encyclopedia. 1905.

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[1] Fletcher, Robert L. (1987). Seaweeds of the British Isles, Volume 3 Fucophyceae (Phaeophyceae). British Museum (Natural History). ISBN 0-565-00992-3.

[Jones_2012-2] Jones VA, Dolan L (July 2012). "The evolution of root hairs and rhizoids". Annals of Botany. 110 (2): 205–212. doi:10.1093/aob/mcs136. PMC 3394659. PMID 22730024.

[3] Demes KW, Littler MM, Littler DS (2010). "Comparative phosphate acquisition in giant-celled rhizophytic algae (Bryopsidales, Chlorophyta): Fleshy vs. calcified forms". Aquatic Botany. 92 (2): 157–160. doi:10.1016/j.aquabot.2009.10.012.

[4] Smith GM (1955). Cryptogamic Botany, Volume 1 Algae and Fungi. McGraw-Hill Book Company Inc.

[5] Lee, Welton L.; Reiswig, Henry M.; Austin, William C.; Lundsten, Lonny (2012). "An extraordinary new carnivorous sponge, Chondrocladia lyra, in the new subgenus Symmetrocladia (Demospongiae, Cladorhizidae), from off of northern California, USA". Invertebrate Biology. 131 (4): 259–284. doi:10.1111/ivb.12001. ISSN 1077-8306.

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