Some of the older systems included
Xeronema in Hemerocallidaceae, but with considerable doubt about whether it really belonged there.
Molecular phylogenetic studies of
DNA sequences have shown that
Xeronema is
sister to a
clade consisting of
Asphodelaceae sensu lato,
Amaryllidaceae sensu lato, and
Asparagaceae sensu lato.
Xeronema is now placed in its own family,
Xeronemataceae. They defined Hemerocallidaceae as consisting only of
Hemerocallis. They excluded
Phormium and its relatives, placing them into a separate family,
Phormiaceae. This treatment was followed by
Armen Takhtajan in 2009, in a classification that was based almost entirely on
morphology and that recognized
paraphyletic groups. It was not followed in a major work on monocot taxonomy which appeared in 1998. The broader version of the family, Hemerocallidaceae
sensu lato, includes those species that would otherwise be assigned to Johnsoniaceae. Johnsoniaceae and Hemerocallidaceae
sensu stricto form a clade that has strong
statistical support. One study found Johnsoniaceae to be
embedded in Hemerocallidaceae
sensu stricto, but this result did not have strong
bootstrap support. The broader version of Hemerocallidaceae is the one that was accepted by the
Angiosperm Phylogeny Group when they published the
APG II system in 2003. When this system was superseded by
APG III in 2009, Hemerocallidaceae was not recognized, instead being treated as subfamily Hemerocallidoideae of the expanded family Xanthorrhoeaceae
sensu lato. ==Genera==