Rhizoids are that extend from the lower epidermal cells of and algae. They are similar in structure and function to the of vascular plant land plants. Similar structures are formed by some fungi. Rhizoids may be unicellular or multicellular.
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.
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.
Land plants
In land plants, rhizoids are
that anchor the
plant to the ground. In the
Marchantiophyta, they are absent or unicellular, but they are multicellular in
. In
, 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.
Microscopic free-floating species, however, do not have rhizoids at all.
Fungi
In
fungi, rhizoids are small branching
hyphae that grow downwards from the
and anchor the fungus to the substrate, where they release digestive
and absorb digested organic material.
See also
-
Rhizine, the equivalent structure in lichens
Further reading
External links
