The basic chromosome number in the majority of Indian taxa (belonging to subgenus Curcuma) is x = 7; published counts correspond to 6x, 9x, 11x, 12x and 15x ploidy levels. Only a few species-specific C-values were found, but karyological and/or flow cytometric data may support taxonomic decisions in some species alliances with morphological similarities. Close evolutionary relationships among some cytotypes are suggested based on the similarity in homoploid genome sizes and geographical grouping. A new species combination, Curcuma scaposa (Nimmo) Skornick. & M. Sabu, comb. nov., is proposed.

Curcuma comprises 120 species that occur throughout tropical and subtropical Asia. The taxonomy of the genus is haunted by polyploid speciation and homoploid hybridization, making it the most challenging genus in Zingibereae (Zingiberaceae). Curcuma is best known for turmeric (C. longa), but numerous species are extensively used as medicinal plants, ornamentals, and sources of starch, among many other uses. The delimitation of the genus has been a matter of dispute since its establishment by Linnaeus (1753), and further conflict has arisen from recent molecular and morphological studies suggesting either paraphyly of Curcuma or the necessity to broaden the genus to include four small genera (Laosanthus, Paracautleya, Stahlianthus, Smithatris) as well as several species currently placed in Kaempferia and Hitchenia. All previous infrageneric classifications were based on limited material that did not include species from the Indochinese f loristic region, and these classifications are unable to unequivocally accommodate all currently known members of the genus. To test the monophyly and delimitation of Curcuma and to gain more insight into infrageneric relationships, three plastid regions (trnL–trnF, psbA–trnH, matK) and the internal transcribed spacer (ITS) of nuclear ribosomal DNA were sequenced. Fifty Curcuma species covering the morphological and geographic variation of the genus and 12 Curcuma–like species currently or previously treated as members of other genera were included in this study. In addition, four Zingibereae and three other Zingiberaceae species were used as outgroups. The results of maximum parsimony and Bayesian analyses clearly support a broad generic boundary for Curcuma, with inclusion of Laosanthus, Paracautleya, Stahlianthus, Smithatris and some species of Kaempferia and Hitchenia (K. scaposa, K. candida, H. caulina, H. glauca). Four main groups in Curcuma s.l. were detected, and their importance for classification at the subgenus level is discussed. A new infrageneric classification is proposed here with a formal description of a new subgenus. Cloning uncovered a broad range of variation of ITS sequences within individuals, particularly in the terminal ‘Curcuma’ group containing representatives of the nominal subgenus Curcuma. This ‘intra–individual ITS polymorphism’ increases with ploidy level and is coupled with preferred vegetative reproduction. Additional studies are needed to further uncover highly complex relationships in this subgenus.

The existence of the type material indicated in the protologues of all Indian Curcuma species names is confirmed or excluded following visits to numerous herbaria. Lectotypes, neotypes and epitypes are designated for previously untypified names or names for which the holotype is missing. Earlier ineffective or superfluous typifications are discussed, several new synonyms are recognised and notes on critical taxa are provided.

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In this paper we provide a thorough overview of past attempts at infrageneric classification of the genus Curcuma (Zingiberaceae). As the recent results of phylogenetic analysis of the genus confirmed that previous infrageneric classifications are not tenable, we provide a revised circumscription of Curcuma with an outline of new infrageneric classification into three subgenera, C. subg. Curcuma, C. subg. Ecomatae and C. subg. Hitcheniopsis including lists of species to be included in each subgenus. Three previously recognized genera, Laosanthus, Smithatris and Stahlianthus, are sunk to Curcuma and two species previously recognized in the genus Hitchenia, H. caulina and H. glauca, are transferred/re-recognized to Curcuma. The previously proposed transfers of the monospecific genus Paracautleya, Hedychium scaposum (Kaempferia scaposa, Monolophus scaposus) and Kaempferia candida, to Curcuma are also confirmed. All connected nomenclatural innovations, corrections and outstanding typifications, inclusive those of infrageneric names, are effected in this paper. A list of excluded names originally described as members of Curcuma, but now accepted as members of other genera is also included.