rhizoid

A rhizoid is a slender, root-like filament that anchors photosynthetic tissue to a substrate and assists in water and mineral uptake. Unlike true roots, rhizoids lack vascular tissue and do not conduct water internally.

Rhizoids can be unicellular or multicellular filaments that originate from the base of a thallus or from a protonemal stage. They grow at their tips and may form a network that helps secure the organism to moist surfaces.

Rhizoids occur in a variety of organisms. In bryophytes (mosses, liverworts, and hornworts) they anchor the gametophyte and assist nutrient absorption. Some algae also develop rhizoid-like structures for attachment, and certain fungi produce rhizoid hyphae that penetrate the substrate to absorb nutrients.

Function and significance: rhizoids provide anchorage and surface absorption, enabling growth in terrestrial or shoreline habitats where water is available from the substrate. They are not vascular tissues, and they do not form a true root system.

In evolutionary terms, rhizoids represent an early adaptation for substrate attachment and nutrient uptake prior to the evolution of true roots with vascular tissue.