Hemerocallidaceae is a recent segregate of the family Liliaceae. It's taxonomy is rather complicated. The APG system placed only 1 genus Hemerocallis into this family, in which case there are 16 species. However, the APG II system included this family in the Xanthorrhoeaceae but allowed for it's segregation into Hemerocallidaceae. Therefore, depending on what system you use, the distribution of this family can be rather broad.
For our geophyte purpose, the following information pertains to the family Hemerocallidaceae with only the genus Hemerocallis included: Plants are glabrous herbs with rhizomatous or tuberous root systems. The leaves are aggregated at the base. They are restricted to the Holarctic. Japan seems to be the center of diversity for this family.