Polyploidy is common in the ginger family Zingiberaceae. The aims of the present paper are (1) to provide a general introduction on species diversity with emphasis on conservation; (2) to highlight the human-use significance of this family, focusing on the two major genera, Zingiber (ginger) and Curcuma (turmeric); (3) to present chromosome number data from 45 natural and cultivated Curcuma taxa from Thailand, of which polyploids are predominant; and (4) to describe our own work on cytotaxonomy of selected Thai Curcuma species. We obtained somatic chromosome numbers from root tips and analysed meiotic chromosome behaviour from flowers. We also used the molecular cytogenetic method of ribosomal gene mapping on chromosomes to infer mechanism of polyploidization and reveal genomic relationships among closely related species. The main results of our cytogenetic studies include the following. The most sought-after medicinal Curcuma cultivars growing on a large-scale basis are secondary triploids, so as taxa in natural habitats that are harvested for local utilisation. These triploids are sexually deficient, due to meiotic pairing abnormalities, but they are propagated asexually via rhizomes. The ribosomal mapping results indicate natural triploidization process via hybridisation, either within populations or across the species boundaries.

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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.

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Gagnepainia godefroyi K. Schumann, 1904 and G. harmandii K. Schumann, 1904 belong to the genus Gagnepainia K. Schumann, 1904 of the Ginger family. They have the potential to be developed as medicinal and attractive ornamental plants. To date, the knowledge on the cytological and reproductive aspects of Gagnepainia have not been publicly available. Therefore, the aims of this research are to investigate the cytogenetic and pollen characters of Gagnepainia species using light, fluorescence, and scanning electron microscopes. The regular meiotic figures of 15 bivalents are found in both species and presented for the first time. These evidences indicate that Gagnepainia is diploid and contains 2n = 2x = 30 with basic number of x = 15. The mean nuclear DNA contents range from 1.986 pg in Gagnepainia sp., 2.090 pg in G. godefroyi to 2.195 pg in G. harmandii. Pollens of all species are monad, inaperturate, prolate with bilateral symmetry, and thick wall with fossulate exine sculpturing. The pollen size of G. harmandii (74.506 ± 5.075 μm, 56.082 ± 6.459 μm) is significantly larger than that of G. godefroyi (59.968 ± 3.484 μm, 45.439 ± 2.870 μm). Both 2C DNA content and pollen size are the effective characteristics for species discrimination. The reproductive evidence of high meiotic stability and normal pollen production indicate that both Gagnepainia species have high fertility and seed productivity, which are in accordance with the broad distribution. The present study provides good cytogenetic and pollen characters not only for plant identification, but also plant fertility assessment through plant genetic resource management and improvement of Gagnepainia.

The genus Paris is an important and confusing taxon due to high variation within species, and differences between species are sometimes difficult to delimit. Thus, the status of some taxa has changed over time. To clarify the status of Paris species for plant conservation and effective management of this genus in Thailand, we performed an intensive survey in northern Thailand, studied morphological characteristics, and constructed a molecular phylogenic tree, which we compared to recently published results of this genus. Our results indicate that there are two species in Thailand: P. yunnanensis and a new species, P. siamensis. Detailed descriptions, illustrations, and the phylogenetic position of these two species are provided here.

Hedychium longicornutum Griff. ex Baker is a Zingiberaceous plant that has been used for traditional medicines and ornamental purposes. Though this plant is a vulnerable plant of Thailand, it has a high potential to be promoted as a new economic ornamental plant due to its exotic inflorescences. However, the usage of this valuable plant on a large scale is restricted since the population of H. longicornutum in natural habitat is limited. This current study established a micropropagation protocol to ensure sustainable use of this plant for commercial and conservation purposes. In vitro axenic plants of H. longicornutum were initiated from seeds. Optimum shoot multiplication medium was evaluated by culturing leafy-shoot bases on Murashige and Skoog’s (MS) medium supplemented with 0-35 µM of N6-benzyladenine (BA) or thidiazuron (TDZ). BA supplemented media were better than those TDZ media since no abnormalities of shoot morphology, shoot elongation, and root regeneration were found. MS supplemented with 15 µM BA was revealed to be the most effective medium for shoot multiplication (9.75 leafy-shoots/explant with 9.54 cm height). Regenerated shoots spontaneously rooted on MS medium. The in vitro raised plants were successfully grown ex vitro and showed the highest survival rate (100%) on planting substrate consisting of 2 garden soil mixture: 1 smashed charcoal. The genetic fidelity of the micropropagated plants compared with mother plants grown in the field was assessed by random amplified polymorphic DNA (RAPD) technique. The results consistently demonstrated the genetic uniformity of the regenerants. This is the first report of an established in vitro true-to-true type propagation in H. longicornutum.