1. One of a group of delicate and often colourless hairlike outgrowths found in certain algae and the gametophyte generation of bryophytes and ferns. They anchor the plant to the substrate and absorb water and mineral salts.

2. A modified hypha found in certain fungi that serves to anchor the fungus to the substrate, and in some cases to secrete digestive enzymes and absorb the solubilized nutrients.