Curcuma L. is an economically important genus in the family Zingiberaceae. Many species are grown as medicinal, culinary, and ornamental crops. As a result of their high morphological diversity and small chromosome sizes, chromosome numbers and species relationships of Chinese Curcumas remain debated. This study examined chromosome numbers of 15 populations representing 11 species of Curcuma from China. Results showed that only Curcuma flaviflora S. Q. Tong was diploid with 2 n = 2 x = 42 and C. kwangsiensis S. G. Lee & C. F. Liang was tetraploid with 2 n = 4 x = 84. The other species were triploid (2 n = 3 x = 63). The study indicated that the basic chromosome number of Curcuma from China could be x = 21. The diploid C. flaviflora produced viable seeds, which was the main means for propagation. The tetraploid and the triploids produced no seeds and relied on rhizomes for propagation. Chromosome sizes of all species were small, ranging from 0.5 to 2.1 μm, which prevented karyotype analysis. The fact that nine of 11 species studied were triploid indicates that triploidy may have some type of competitive advantage over the diploid and tetraploid. In addition, the triploids are popular commercially because of abundant rhizome production and this may contribute to their wide distributions.

Zingibereae is a large tribe in the family Zingiberaceae, which contains plants with important medicinal, edible, and ornamental values. Although tribes of Zingiberaceae are well circumscribed, the circumscription of many genera within Zingibereae and the relationships among them remain elusive, especially for the genera of Boesenbergia, Curcuma, Kaempferia and Pyrgophyllum. In this study, we investigated the plastome variation in nine species representing five genera of Zingibereae. All plastomes showed a typical quadripartite structure with lengths ranging from 162,042 bp to 163,539 bp and contained 132–134 genes, consisting of 86–88 coding genes, 38 transfer RNA genes and eight ribosomal RNA genes. Moreover, the characteristics of the long repeats sequences and simple sequence repeats (SSRs) were detected. In addition, we conducted phylogenomic analyses of the Zingibereae and related taxa with plastomes data from additional 32 species from Genbank. Our results confirmed that Stahlianthus is closely related to Curcuma, supporting the idea of merging it into Curcuma. Kaempferia, Boesenbergia and Zingiber were confirmed as close relatives and grouped together as the Kaempferia group. Pyrgophyllum is not allied with the Curcuma clade but instead is embedded within the Hedychium clade. Our results demonstrate the power of plastid phylogenomics in improving the phylogenetic relationships within Zingibereae and provide a new insight into plastome evolution in Zingibereceae.

Previous studies recognized three major lineages of the family Costaceae: a South American clade, an Asian clade and a Costus clade. However, the genus Hellenia within the Asian clade has been shown to be non-monophyletic and its morphology has not been studied carefully. Therefore, the complete plastid genomes of Hellenia species were obtained and the monophyly of Hellenia was tested through four different datasets in this study. Plastid phylogenomic analyses of Costaceae revealed that Hellenia is strongly supported as paraphyletic. Two major clades are recovered, namely the Hellenia s.s. subclade and the Parahellenia subclade. Phylogenetic analyses based on an enlarged taxon sampling of the Asian clade using a two chloroplast markers dataset (trnK intron and trnL-F spacer) confirmed the paraphyly of Hellenia. Meanwhile, morphological analyses suggested that members of the Parahellenia subclade differ from the remaining Hellenia species in many characters including inflorescences, bracts, stigma, axillary buds, floral tubes and labellum. According to the present molecular and morphological evidence, the latter subclade is recognized as a new genus, Parahellenia. Two new species are described, four new combinations are made, and identification keys are also provided.

Costus chinensis and C. oblongus (Costaceae) has been previously placed in synonymy under C. lacerus. Our critical examination of herbarium specimens including type material demonstrates that they are morphologically distinct from each other. Therefore, the independent specific status of C. chinensis and C. oblongus is reinstated. According to recent studies, Costus chinensis as well as other two Chinese species, C. oblongus and C. viridis, should be transferred to Hellenia. Thus, a new name for C. chinensis, and two new combinations are proposed. A detailed description of C. chinensis along with a distribution map of three allied species is also provided.