Is this for the Daily telegraph crossword by anychance? The answer is rhizzoid.
lichen
Mutualism.
Lichen is the base in the chain of succession. It starts at lichen, the moves on to moss, then to small plants, and so on.
Symbiosis
lichen
Moss. lichen
lichen and other sea plants
Moss and lichen prepare area for other organisms.
lichen
lichen
No, lichen is a composite organism of symbiotic fungi with alga or cyanobacteria (single cell plants).
Lichen is a mixture of algae / cyanobacteria and fungi. Lichens may look like plants but they do not reproduce with flowers. Lichens do not have roots like plants. They grow on plants as a substrate not as a parasite.