Kaempferia aurora Noppornch. & Jenjitt., from Tak province near the Thailand-Myanmar border, and K. caespitosa Noppornch. & Jenjitt., from Lampang province, Northern Thailand, are described as new species of subgenus Protanthium (Horan.) Baker. The diagnostic characters are clearly compared with the similar species. Detailed illustrations, photographs of floral dissection, information of phenology, distribution and ecology, and preliminary conservation status are provided for each new taxon. An identification key to the species of Kaempferia subgen. Protanthium in Thailand are also revised and presented.

Field studies have been conducted throughout Northern Thailand and living materials of each new taxon were collected. The morphological and phenological characters were mainly obtained through the study of living specimens in their natural habitat and in cultivation, especially the Ginger and rare plant nurseries at QSBG in Chiang Mai, Thailand. Protologues and herbarium specimens of Kaempferia subgen. Protanthium held in BK, BKF, QBG, SING, Suan Luang RAMA IX herbarium, and several online herbarium specimen databases, especially Kew Herbarium Catalogue and Chinese Virtual Herbarium (CVH) were also intensively examined. Taxonomic descriptions, flower dissection, distribution and ecology information, detailed photographs and line illustration, and preliminary conservation status were carried out and provided for each new species. Diagnostic morphological and flowering phenological characteristics of new taxa were compered with the close morphologically similar species. A key to identification of the species of Kaempferia subgen. Protanthium was reconstructed, modified from Nopporncharoenkul & Jenjittikul (2017). Type specimens with duplicates were prepared and deposited at BK, BKF, QBG, and SING.