The Amarylliaceae J.St.-Hil., a cosmopolitan family of petaloid monocots, represents one of the elements of Hexandra monogynia (Linnaeus, 1753), including 51 genera. These genera were generally classified into two main groups: Liliaceous and Amaryllidaceous groups, based primarily on the position of ovary. All of these genera were sometimes treated under the broad sense of Liliaceae. The Amaryllidaceous genera have since been included within various common taxonomic units such as section Narcissi (de Jussieu, 1789), family Amarylleae (Jaume-St.-Hilaire, 1805; Brown, 1810), natural order Amaryllidaceae (Lindley, 1836), tribe Amarylleae (Benthum & Hooker, 1883), suborder Amarylleae (Baker, 1888), family Amaryllidaceae (Hutchinson, 1934) and subfamily Amarylloideae (Melchior, 1964).
The genera with superior ovary were excluded from Amaryllidaceae by Brown (1810). Hutchinson (1934) reclassified the Amaryllidaceae by defining the diagnostic features of the family as an umbellate inflorescences subtended by one or more spathaceous bracts. Agavaceae, Hypoxidaceae and Alstromeriaceae were segregated, but Alliaceae was included in Amaryllidaceae. Taktajan (1969), Dahlgren et al. (1985) and Heywood et al. (2007) recognized Amaryllidaceae in a narrow sense, maintaining a distinct family Alliaceae. However, Thorne (1976) and Cronquist (1981) placed Amaryllidaceae within Liliaceae s.l.
The Amaryllidaceae is treated here in a narrow sense, posses a bulbous rootstock, an umbellate inflorescence or solitary flower, with one to few spathes and with inferior ovary (Taktajan, 1969). Two genera are native to Thailand. Keys to the genera and species, also the descriptions of all taxonomic units are based on Thai specimens from the following herbaria: BCU, BK, BKF, CMU, E , K, KKU P and QBG.