1.	Obligatory coprophilous species; sporangiophores bearing subsporangial vesicles and trophocysts	2
1.	Facultative coprophilous species; sporangiophores without subsporangial vesicles and trophocysts	6
2.	Sporangiospores globose, subglobose or ovoid	3
2.	Sporangiospores ellipsoid	5
3.	Subsporangial vesicles ovoid; sporangiospores globose or subglobose, thin-walled	4
3.	Subsporangial vesicles obovoid; sporangiospores thick-walled, spherical to broad ovoid	Pilobolus oedipus
4.	Trophocysts short, 180–610 × 125–270 μm; columellae cylindrical; sporangiospores subglobose, 7–11 μm in diam.	P. minutus
4.	Trophocysts long, 410–1800 × 240–420 μm; columellae conical; sporangiospores subglobose, 10–18.5 μm in diam.	P. longipes
5.	Columellae nipple-like; sporangiospores ellipsoid, pale yellow or hyaline 7.5–12 × 4.5–6.5 μm	P. crystallinus
5.	Columellae conical-cylindrical; sporangiospores ellipsoid, intensely yellow 10.5–17.5 × 5.5–8 μm	P. kleinii
6.	Sporangiophores bearing sporangia	8
6.	Sporangiophores bearing merosporangia or sporangiola	7
7.	Merospores produced in merosporangia	Syncephalastrum racemosum
7.	Pedicellate unispored sporangiola produced on a fertile vesicle	Cunninghamella echinulata var. echinulata
8.	Sporangiophores simple or with erect or curved branches; sporangia without sterile spines	9
8.	Sporangiophores with circinate branches; sporangia with a sterile spine	Circinella muscae
9.	Sporangia unapophysate; giant cells not produced	10
9.	Sporangia apophysate; giant cells present or absent	20
10.	Sporangiospores regular in shape and size	11
10.	Sporangiospores with varied shapes and sizes, globose, ovoid, cylindrical or fusiform	Mucor variosporus
11.	Sporangiophores unbranched or slightly branched	12
11.	Sporangiophores repeatedly branched	13
12.	Columellae obovoid; sporangiospores ellipsoidal, plano-convex 2.5–10 × 2–7.5 μm	M. hiemalis
12.	Columellae globose; sporangiospores long-elliptical and fusiform 2.5–8.1 (–12.5) × 1–5 μm	M. luteus
13.	Mesophilic species, not growing at 40 °C	14
13.	Thermotolerant, growing at 40 °C	M. indicus
14.	Columellae regular in shape; sporangiospores globose, subglobose or ellipsoid	15
14.	Columellae of several shapes; sporangiospores subspherical to ellipsoid	Mucor sp.
15.	Sporangiophores with swellings or not; sporangia with short lateral branches; columellae flattened, globose or obovoid; chlamydospores present or not, when present never abundant and never formed in reproductive structures	16
15.	Sporangiophores without swellings and with long lateral branches; columellae subglobose, ovoid or ellipsoid; abundant chlamydospores produced in sporangiophores and in a few columellae	M. racemosus f. racemosus
16.	Colonies high (up to 10 mm); sporangiophores curved or not; swellings under sporangia absent; columellae obovoid, globose or subglobose	17
16.	Colonies low (up to 2 mm); sporangiophores curved or not; swellings often viewed under sporangia; columellae flattened	M. ramosissimus
17.	Colonies initially white, turning gray in older cultures; sporangiophores up to 7 (–10) μm in diam.; sporangia black	18
17.	Colonies initially yellow, turning brownish in older cultures; sporangiophores up to 14 (–17) μm in diam.; sporangia gray-brownish	19
18.	Sporangiophores sympodially branched; dark sporangia, globose (15–) 20–72.5 (–75) μm; sporangiospores ellipsoid	M. circinelloides f. griseo-cyanus
18.	Sporangiophores sympodially or monopodially branched (rarely); sporangia dark brown, globose to slightly subglobose, 20–90 μm; sporangiospores globose to slightly subglobose	M. circinelloides f. janssenii
19.	Sporangia dark brown and globose, 35–85 μm; columellae obovoid; sporangiospores ellipsoid	M. circinelloides f. circinelloides
19.	Sporangia brown and globose, 21.5–92.5 μm; columellae globose; sporangiospores ellipsoid and sometimes irregularly shaped	M. lusitanicus
20.	Sporangiophores arising from stolons, never opposed to rhizoids, spherical sporangia, piriform or subpiriform and apophysed; giant cells present	21
20.	Sporangiophores arising from the aerial mycelium and/or stolons, opposed to rhizoids, sporangia apophysed, globose and subglobose; giant cells absent	23
21.	Thermophilic species, growing at 40 °C; subsporangial septum absent or rare; sporangiospores globose, subglobose or ellipsoid; giant cells present	22
21.	Mesophilic species, not growing at 40 °C; subsporangial septum present; sporangiospores cylindrical; giant cells absent	Absidia cylindrospora var. cylindrospora
22.	Columellae globose, subglobose and spatulate, often exhibiting projections; giant cells present	Lichtheimia ramosa
22.	Columellae subglobose and short hemispheric, without projections; giant cells absent	L. brasiliensis
23.	Rhizoids present, well developed, abundant and rhizopodiform; sporangiophores reaching 3 mm in length; columellae ovoid	Rhizopus stolonifer
23.	Rhizoids, undeveloped, simple or rarely branched when present; sporangiophores reaching 1.7 mm in length; columellae subglobose, hemiglobose, rarely oblong-ovoid	R. arrhizus var. arrhizus