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 Xanthorrhoeaceae sensu lato, Amaryllidaceae sensu lato, and Asparagaceae sensu lato. Xeronema is now placed in its own family, Xeronemataceae.
In 1985, Dahlgren, Clifford, and Yeo produced a work on monocot taxonomy that remained influential for over two decades. 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.
In the 21st century, Hemerocallidaceae has been defined in essentially two different ways in systems based on monophyletic groups. In the narrower of these circumscriptions, Hemerocallidaceae sensu stricto, it consists of 12 genera and 40 to 50 species. It does not include the 8 genera and about 38 species that are placed in a separate family, Johnsoniaceae.
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 When this system was superseded by APG III in 2009, Hemerocallidaceae was not recognized, instead being treated as subfamily Hemerocallidoideae of the expanded family Xanthorrhoeaceae sensu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.
For a phylogeny of Hemerocallidaceae, see the phylogenetic tree at Xanthorrhoeaceae.
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