The genus Acis was defined in 1807 by Salisbury. 80 years later it was lumped into Leucojum and remained there for many years. Generations of gardeners came to know species all as Leucojum. In 2004 an extensive study by Lledo and co-workers* concluded that Acis was after all distinct from Leucojum and separated them again.
Leucojum now comprises just two species, aestivum and vernum, closely related to Galanthus. The 10 smaller species with narrow, thread-like leaves, solid (not hollow) flower stems and flowers without green markings are now Acis.
Some species moved from Leucojum to Acis have slight name changes, usually just a gender agreement, thus Leucojum roseum becomes Acis rosea etc. There has been a rethink of Greek plants formerly ascribed to L. valentinum.
*Lledo, Davis, Crespo, Chase and Fay. "Phylogenetic analysis of Leucojum and Galanthus (Amaryllidaceae) based on plastid matK and nuclear ribosomal spacer (ITS) DNA sequences and morphology". Plant Systematics and Evolution, July 2004.
Order (early) from Autumn list only.