Several Kaempferia species, endemic to Thailand, are rare and therefore entitled to conservation status; other species are widely cultivated. We conducted extensive cytogenetic investigation of this genus to elucidate the botanical and taxonomic characterization of these plants. The study included 42 accessions belonging to 15 Kaempferia species and four undescribed taxa from regions throughout Thailand, and one species from Laos. We determined chromosome numbers from root‐tip cells collected from germinating rhizomes ex situ, but examined meiosis in flowers collected from the wild. The mitotic analyses verify that 2n chromosome numbers range from 22 (diploid, 15 taxa), 33 (triploid, three species), 44 (tetraploid, five taxa) to 55 (pentaploid, one species). Four taxa included accessions with different ploidy levels. The meiotic analyses demonstrated that all 14 diploid accessions investigated displayed normal meiosis, forming 11 bivalents, indicating the base chromosome number x = 11 for this genus. Meiotic figures were obtained from one triploid and four tetraploid accessions. The triploid showed 11 trivalents, most likely indicating autotriploidy. Two tetraploid accessions showed regular meiotic figures consisting of 22 bivalents, probably indicating allopolyploidy originating from interspecific hybrids, a hypothesis that is consistent with observations of plant morphology. The other two tetraploid accessions belong to the same species and show mostly irregular meiotic figures. Cytogenetic information is useful for evaluating fertility and hybridity in the genus. Good seed set was observed among diploid and tetraploid accessions. Triploid and pentaploid plants, on the other hand, do not set seeds, but produce large clusters of vegetatively‐propagated rhizomes.

Kaempferia noctiflora, another precocious flowering species of Kaempferia subgen. Protanthium (Zingiberaceae) from Northern Thailand is described and illustrated. Pure white flowers with nocturnal anthesis and a tinged purplish red patch along the midvein of the upper surface of the leaves are the unique characters of this new taxon. The morphological characters of K. noctiflora are compared to closely related species and a key to Thai precocious flowering Kaempferia species is also provided.

Kaempferia jenjittikuliae, a new species of Kaempferia subg. Protanthium (Zingiberaceae) from Central–Northeastern Thailand, is described and illustrated. The diagnostic characters of this novel taxon are discussed and compared with those of the morphologically similar species Kaempferia lopburiensis, K. rotunda and K. udonensis. Detailed photographs of plants and dissected flowers, and information on phenology, distribution and ecology, are provided. A preliminary IUCN conservation assessment of Critically Endangered (CR) is assigned.

Kaempferia aurora sp. nov. Noppornch. & Jenjitt., from Tak province near the Thailand‐Myanmar border, and K. caespitosa sp. nov. Noppornch. & Jenjitt., from Lampang province, northern Thailand, are described as new species of K. subgen. Protanthium (Horan.) Baker. Their diagnostic characters are compared with those of similar species. Detailed illustrations, photographs of dissected flowers, information on phenology, distribution and ecology, and preliminary conservation statuses are provided for both new species. An identification key to the species of Kaempferia subgen. Protanthium in Thailand is also revised and presented.

Curcuma candida is a conservation-vulnerable species, rare and endemic to the Tenasserim Range (Thio Khao Tanaosri). This species was initially classified into the genus Kaempferia, based on morphology of specimen from Myanmar, and was given the name K. candida in 1830, but the first specimen from Thailand was only discovered in 2000. With the addition of molecular evidence, the species was transferred to Curcuma. The aim of the present study was therefore to find cytogenetic identity of C. candida, by investigating mitotic and meiotic divisions of five accessions obtained from the border districts of Thailand and Myanmar, in comparison with previous cytogenetic records of Curcuma and Kaempferia. The results show that C. candida is diploid with 2n = 42 and there is no variation among accessions. All accessions showed meiotic figure representing 21 bivalents during microsporogenesis, indicating the secondary base number x = 21. These chromosomal characteristics are closely similar to those found in diploid Curcuma species. The present paper also includes field observation and description of the plant phenology. The work has underlined an urgent need to protect this species in nature. During the sample collection trips we witnessed an excessive collection of edible flowers for local consumption.