Calcium oxalate crystals occur on the sporangiolar appendages and aerial hyphae of the two known genera (Hesseltinella, Radiomyces) of the mucoralean family Radiomycetaceae. In Hesseltinella the sporangiolar appendages are acicular with a polygonal, square, or hexagonal, discoid base. The appendage core consists of calcium oxalate and is composed of two portions: (1) a round, acicular spine with a more or less hexagonal base, and (2) a square, polygonal, or hexagonal, discoid base with a central perforation that generally contains the spine base. Both portions of the spine core appear to be readily separable. In species of Radiomyces the appendages are capitate with a crystal embedded in the distal, inflated end. Hyphal crystals bearing a short spine are similar in morphology to the sporangiolar appendages and are regularly produced by Hesseltinella. Initially these crystals are embedded in the hyphal wall. First, the spine is extruded out. Then some of the wall material is lost, exposing the base, a process concurrent with dehiscence of the crystal spine. In Radiomyces, the young aerial hyphae are typically smooth but calcium oxalate crystals were observed on aging mycelia.
Benny, G. L. and Khan, S. R.
"The Radiomycetaceae (Mucorales; Zygomycetes). Calcium Oxalate Crystals on the Sporangiolar Wall and Aerial Hyphae,"
Scanning Microscopy: Vol. 2
, Article 52.
Available at: https://digitalcommons.usu.edu/microscopy/vol2/iss2/52