Description of the fungus

• The mycelium of Rhizopus stolonifer consists largely of syphonized hyphae that grow rapidly. It is from these brown hyphae that the develop runners , characteristic curved hyphae, at the origin of the species name of this Rhizopus . When the runners come into contact with the substrate of the fungus (here: the cluster), they then produce branched rhyzoids (figures 1 and 2) from which the sporangiophores will leave in the opposite direction (figures 3 to 7).
• The sporangiophores brown are isolated or gathered in sparse tufts. Up to 3.5 mm long and 20-34 µm wide, these structures, at the end of which are the sporangia , are easily visible with a binocular magnifying glass. The sporangia appear as black globular vesicles with a diameter of between 40 and 350 µm, with a flattened base.
• It is from these sporangia that are produced sporangiospores celled, hyaline to brown. These spores, round to ovoid (4-11 µm in diameter), have a slightly striated surface (figure 8).
• Note that the sporangia of R. stolonifer have a columella and a process whose collapse after release of the spores gives rise to an umbrella-like structure (Figure 9).
• Sexual reproduction allows the formation of zygospores black, globular, relatively large (100-180 µm), and brown to black, ornamented .
• Appearance of colonies on malt-agar medium : they spread rapidly and have a cottony white appearance, then gray when sporulation occurs (figure 10). The reverse side of the colony is also white.