The genus
Donatia is sometimes included in Stylidiaceae in the monogeneric subfamily
Donatioideae. The
APG II system recommends its inclusion in Stylidiaceae but allows for the optional recognition of the family
Donatiaceae. Molecular and
phylogenetic analysis have determined that
Donatia is a sister-group to Stylidiaceae and therefore placing
Donatia in its own family has been recommended by several authorities. Including
Donatia within the Stylidiaceae would endanger its status as a
monophyletic group. Donatioideae and Stylidioideae were described by
Johannes Mildbraed in his 1908 taxonomic monograph of the family. The subfamilies were created to distinguish the difference between the five typical
genera of the Stylidiaceae from the single genus
Donatia, which Mildbraed placed in Donatioideae. The subfamily taxonomy represents the taxonomic uncertainty of
Donatia, which has often been placed in its own family, Donatiaceae, or other families such as the
Saxifragaceae. Mildbraed's classification also included two
tribes: Phyllachneae, which included the genera
Forstera and
Phyllachne, and Stylidieae, which included
Levenhookia,
Oreostylidium, and
Stylidium. This level of infraspecific taxonomy is not used in recent research, but the groupings are supported by molecular data that suggest
Forstera and
Phyllachne are closely related but distinct from the other three. APG II places Stylidiaceae and Donatiaceae in the
Asterales. The
Cronquist system placed both families in the
Campanulales. The
Takhtajan and
Reveal systems place both families in the order Stylidiales. The
Dahlgren system uses the same Stylidiales order, but it omits Donatiaceae. The
Thorne system shifts Stylidiaceae into the
Saxifragales order. ==References==