Table 6.

Differentiating features of the main Rhizopusspecies and groups causing disease in humans

Organism nameColony morphologySporangium morphologyApophysis and columella morphologySporangiospore morphology
R. stolonifer“Lid-lifting” floccose white mycelium with black dots; rapid growthGlobose; black; large (up to 275 μm)Together are oval to subglobose, 70–120 μm in diameter; pale brown; apophysis is distinctRound to oval; black; prominent striations
R. arrhizusFloccose, yellowish-brown colonies, darkening and collapsing with age; rapid growthGlobose; powdery and gray to black; intermediate in size, 100–200 μm in diameterTogether are globose to oval, 40–75 by 60–130 μm; apophysis is inconspicuous; often collapses at sporulationOval to ellipsoidal, 6–8 by 4.5–6 μm; striated
R. microsporus groupModerately floccose mycelium; color varies with varietyGlobose; small (usually about 100 μm)Collumellar shape and size vary among varieties; apophysis is discreteVariable size and shape depending on variety
R. azygosporusFloccose white mycelim, turns grey to black with ageGlobose; small (50–100 μm in diameter)Oval collumellaOval, faintly striated, 4–6 μm
R. schipperaeThin white nonsporulating mycelium on routine mediaGlobose; small (<80 μm in diameter)Subglobose to conical columella; distinct apophysisOval and faintly striated, 4–7 μm
RhizoidsSporangiophore morphology  ZygosporesOther
Abundant; intensely ramified, 300–350 μm longLong (up to 2 mm), pigmented, and unbranched; occur in groups of 1–3Heterothallic; black, round zygospores with irregular surface decorations; 150–200 μm wide; equal suspensorsNo growth at >33°C; good sporulation at 15–30°C
Abundant; brown, with 4–8 branchesIntermediate length (750–2,000 μm, generally 1,500 μm); occur singly or in groups  Heterothallic; reddish brown round to flattened with conical projections; usually 80–140 μmNo growth at >46°C
Simple, no branchingShort (usually 800–1000 μm or less)Heterothallic; Small (80 to 100 μm) red-brownMaximum temperature of growth varies with variety  
Simple, pale brownShort (usually 350–500 μm)Azygospores 30–70 μm in diameter are abundantOptimal growth and sporulation at 25–30°C
Simple, brown, rarely branchedShort (100–410 μm) in clusters of 10Not known; produces many chlamydosporesNo growth at >50°C