Table 2.

Identification key for species of Backusella in the Americas.

1. Sporangiola formed	2
1. Sporangiola not formed	B. oblongielliptica
2. Unispored sporangiola abundant	B. circina
2. Unispored sporangiola rare or not formed	3
3. Giant cells formed	4
3. Giant cells not formed	5
4. Columellae of sporangia ellipsoidal, cylindrical, rarely pyriform; chlamydospores absent	B. gigacellularis
4. Columellae of sporangia conical (majority), but also ellipsoidal with a truncate base, globose to subglobose, subglobose to conical, or, rarely, conical or cylindrical with slight constriction at the center; chlamydospores abundant	B. brasiliensis
5. Azygospores formed	B. azygospora
5. Azygospores not formed	6
6. Sporangiospores ellipsoidal	7
6. Sporangiospores not ellipsoidal	8
7. Sporangia up to 150 (–200) μm diam.; sporangiospores 20–26 × 10–12 μm	B. recurva
7. Sporangia up to 100 (–125) μm diam.; sporangiospores 11–15 × 7–9 μm	B. variabilis
8. Sporangiophores forming a terminal sporangium and few lateral pedicellate sporangiola	B. lamprospora
8. Sporangiophores forming a terminal sporangium with no lateral pedicellate sporangiola	9
9. Columellae of sporangia of varied shapes, some arranged obliquely on the sporangiophores, some with one side more swollen than the other; sporangiospores globose to subglobose	B. obliqua
Columellae of sporangia conical and cylindrical, sometimes constricted at the center, never arranged obliquely on the sporangiophores nor with one side more swollen than the other; sporangiospores subglobose to ellipsoidal, some slightly irregular	B. constricta