Pound (1894) Phycomyces agaricicola Boedijn (1958) Spinellus fusiger, commonly known as bonnet mold,[1] is a species of fungus in the phylum Mucoromycota.

[3] The species was first described by German naturalist Christian Gottfried Ehrenberg in 1818 as Mucor rhombosporus, but he later conceded to making a mistake in examining the spores.

[5] During the reproductive phase of its life cycle, Spinellus fusiger grows throughout the cap of the mushroom host, eventually breaking through to produce radiating reproductive stalks (sporangiophores) bearing minute, spherical, terminal spore-containing structures called sporangia.

Ultimately, the spores in the sporangia are released after the breakdown of the outer sporangial wall, becoming passively dispersed to new locations via wind, water, and insects.

[6] Like other Spinellus species, S. fusiger is homothallic, and sexual spores known as zygospores are produced following the union of branches called gametangia, that arise from the same mycelium.