As of March 2014, the World Checklist of Selected Plant Families accepts the following nine species, one with three subspecies:

Nordal and Duncan explored the relationship between eight of the species in a 1984 analysis based on morphological features (the little-known Scadoxus longiflorus was excluded).
Their preferred cladogram was:
The main division is between a group which does not have bulbs, only rhizomes, and one which has bulbs, usually with rhizomes as well.
As of March 2014, the World Checklist of Selected Plant Families accepts the following nine species, one with three subspecies:

Nordal and Duncan explored the relationship between eight of the species in a 1984 analysis based on morphological features (the little-known Scadoxus longiflorus was excluded). Their preferred cladogram was:
The main division is between a group which does not have bulbs, only rhizomes, and one which has bulbs, usually with rhizomes as well.
Scadoxus