Table 9.

Differentiating features of the Mucor species pathogenic to humans

Organism nameColony morphology  Sporangium morphologyColumella morphology
Mucor circinelloidesFloccose with rapid growth; pale gray to yellowish, brown at 37°CGlobose, 25–80 μmSpherical, up to 50 μm in diameter; collars may be present    
Mucor hiemalisSparse growth; grayGlobose, up to 60 μmEllipsoidal; 15–30 μm in diameter  
Mucor rouxianusDelicate low colonies (4 mm high); white, yellow, or grayGlobose, gold-brown to yellow, usually 50 μm in diameterFlattened or round, up to 40 μm high, colored membrane  
Mucor racemosusLow to medium-high colonies; light to medium brownGlobose, light brown, encrusted walls, up to 80 μmEllipsoidal to pyriform, up to 40 μm long  
Mucor ramosissimusRapidly growing low colonies; gray to buffGlobose, 15–70 μmRound to flattened, 20–37 by 17–30 μm; collars may be seen; smaller sporangia lack columella
Sporangiospore morphologyRhizoids and apophysesSporangiophore morphologyZygospores and chlamydoconidiaOther
Smooth walled and oval; 4.4–7 μmAbsentSympodially branched and circinateHeterothallic; round, red to dark brown, with stellate spines up to 100 μm wide; chlamydoconidia sometimes seenGrowth from 5 to 37°C
Hyaline; smooth walled and oval or reniform; 5–11 μmAbsentBranched or unbranchedHeterothallic; chlamydoconidia rarely producedGrowth up to 32°C
Oval, smooth walled; 4–5 μmAbsentMinimally branchedNo zygospores; many black chlamydoconidia up to 100 μm wideGrowth from 9 to 45°C; optimal growth at 37°C
Oval to subspherical, smooth walled; 5–8 μmAbsentBranchedHeterothallic; abundant chlamydoconidia producedOptimal growth at 25°C, poor or no growth over 32°C
Oval to round, smooth walled, brownish; 3.3–5.5 by 3.5–8 μmAbsentSympodially branched; may have racquet-shaped swellingsZygospores and chlamydoconidia not seen; oidia may be presentOptimal growth at 24°C, poor growth at 37°C