Phycomyces starts its vegetative life cycle as a spore, with three nuclei in average, that germinates after a heat-shock or after exposure to certain chemicals in the presence of suitable nutrients. After activation, the spore will swell and will produce one, two, or sometimes three germination tubes. The germination tubes will grow at their tips, branching repeatedly to form lateral tubes. The resulting tubes, hyphae, will form a thread-like structure, the mycelium that will grow until it occupies the available medium.

Phycomyces hyphae contain no transverse walls (septa), and thus the whole mycelium can be considered as a a single cell (coenocyte). Vegetative reproduction starts with the development of sporangiophores, specialized unbranched hyphae that grow vertically. The nuclei in the hyphae will migrate through the developing sporangiophore and will be packed into spores inside a sporangium, a sphere that is formed at the tip of the sporangiophore. The spores can be liberated from the sporangium and will germinate to create a new mycelium.

There are two types of sporangiophores of very different size, macrophores and microphores. Macrophores can grow for several cm and their growth is very sensitive to external stimuli such as light, wind, barriers, and the presence of nearby objects. The phototropism of the macrophores has been investigated in great detail. Microphores, on the contrary, are about 1 mm long. The number of macro- and microphores that grow in a culture depends on the ambient light: blue light stimulates macrophorogenesis and inhibits microphorogenesis.

There are two sexes in Phycomyces, (+) and (-), with no morphological difference. When hyphae of the two sexes grow close to each other they will slow their growth and will swell, grow, and brach to become zygophores, the first differentiated structures of the sexual cycle. Zygophores have protusions in all directions and a bright colour due to abundant carotene synthesis. Zygophores of opposite sex come into contact to become progamentangia that grow out of the aqueous medium and into the air, as their protusions proliferate and interwine. A gamentangium becomes delimited at the tip of each progamentangium by a transverse septum. The remaining parts of the progametangia are called suspensors, since they support the gamentangia in the air. Thorn-like appendages grow out of the suspensor wall and the two gamentangia mix their contents to form the zygospore. The zygospore remain dormant for months until a germsporangiophore emerges forming a germsporangium containing about 10,000 germspores, similar to the vegetative spores, that are the product of karyogamy and meiosis. The germspores, when placed in appropiate medium, will germinate to form a vegetative mycelium.