Recent scientific studies using DNA sequencing technology have shown that
what we know as Scilla actually appear to have multiple evolutionary
origins. Therefore it seemed reasonable to recognise each coherent group as
separate genera. The following lists these new or resurrected genera that
have been proposed.

Firstly, Scilla lazulina from Zimbabwe appears to be the most primitive
'Scilla'. Was put into Merwilla (see below) before DNA sequencing showed
otherwise. No genus name has yet been proposed.

Pseudoprospero: only 1 species, P. firmifolium. Instantly recognisable in
frequently having a side branch on the flower scape. Summer-growing.
Apparently the second-most primitive of the 'Scillas'.

The remaining 'Scillas' belong to 2 geographical groups: sub-Saharan
African/Indian (which also includes Lachenalia, Ledebouria, Massonia,
Daubenya, Drimiopsis, etc.) and North African/European/Asian (also including
Hyacinthus, Bellevalia, Hyacinthella, Muscari, etc.).

...

The differences between these genera may seem minor, but the only thing they
all have in common is the bluish, star-shaped flowers (which appears to be a
primitive characteristic). Any attempt to reduce the number of genera (by
coalescing related ones) would cause the disappearance of many
well-established ones, as well as making these new super-genera difficult if
not impossible to define.

Definitely controversial!

Julian Slade