Mushrooms

Most fungi develop as hyphae, which are cylindrical, filamentous structures 2-10 µm in diameter and up to a few centimeters long.

An excerpt from the article 22 facts about Mushrooms

The hyphae branch, merge, which leads to the formation of mycelium, which is an interconnected network of hyphae. Many species of fungi develop specialized hyphae structures to take nutrients from living hosts.

Mycelium can form more complex structures that perform specialized functions, e.g. rootstocks, mycelium cords, sclerotia, fruiting bodies.

Fungi do not show differentiation into tissues and organs.