Aletris, containing approximately 21 species, is the largest genus in Nartheciaceae, and is disjunctively distributed in eastern Asia and eastern North America. Its delimitation has been controversial because it is uncertain whether Metanarthecium should be included in the genus. Although there are a few molecular phylogenetic studies on Aletris, the interspecific relationships within the genus have never been evaluated in a phylogenetic context. Here we used two cpDNA loci, matK and trnL-F, to delimitate Aletris and discuss the phylogeny within the genus. Phylogenetic analyses showed Metanarthecium might be distantly related to Aletris. This is also supported by morphological, palynological, cytological, and phytochemical data. Therefore, Metanarthecium should be excluded from Aletris. Within Aletris, there are two major clades： A. farinosa and A. lutea of eastern North America and A. glabra of eastern Asia form clade A; and the remaining Asian species form clade B. The Asian clade includes three subclades： subclade I （two varieties ofA. pauciflora, and A. glandulifera and A. megalantha）, subclade II （three samples of A. laxiflora）, and subclade III （all other sampled Asian species）. Based on phylogenetic relationships, A. pauciflora var. khasiana deserves a specific status, and A. gracilipes, formerly a synonym ofA. laxiflora, should be reinstated. The reconstruction of the perianth evolution indicates that perianth connate halfway and glabrous on abaxial surface are plesiomorphic for Aletris and Nartheciaceae. Farinose-glutinous perianth is a diagnostic character for clade A.
