Boesenbergia monophylla (Zingiberaceae: Zingibereae), a new species from Central Vietnam

Boesenbergia monophylla (Zingiberaceae: Zingiberoideae), a new ginger species from Quang Ngai Province in Central Vietnam, is described and illustrated. The description is accompanied by additional notes on etymology, ecology, phenology, distribution, and preliminary IUCN assessment. The species is unique among all congeners in Cambodia, Laos and Vietnam by its monophyllous habit. For the diagnostic purposes it is compared to Boesenbergia prainiana, another monophyllous species occurring in Peninsular Malaysia and Thailand from which it can be recognised by dark green leaf blades with velvety appearance, petioles as long or longer than half of the length of the leaf blade, largely hidden inflorescence, and flowers pale-yellow with labellum ornamented with red central bands at basal half, widening and turning pink distally all the way to the margin. The novelty brings the total number of Boesenbergia species in Vietnam to seven. An updated key to the species of Boesenbergia in Vietnam is also provided.