Cytotaxonomy of Kaempferia subg. Protanthium (Zingiberaceae) supports a new limestone species endemic to Thailand

Thailand is the biodiversity hotspot of genus Kaempferia (Zingiberaceae) and harbours 14 species belonging to K. subgenus Protanthium. To better understand the taxonomic circumscription and verify the taxonomic status, the present characterization of cytogenetic characters included all recognized and one undescribed species of K. subg. Protanthium from Thailand.

Overall, 88 accessions of plant materials were analysed cytogenetically: 84 and 42 accessions were subjected to flow cytometry and karyology, respectively. Based on genome size and mitotic chromosome numbers, 74 accessions from all species investigated were putative diploid, whereas the others were putative polyploid: triploid (three accessions) and tetraploid (11 accessions). The cytogenetic evidence indicates that 2 n = 2 x = 22 is the diploid number and x = 11 is the base chromosome number for K. subg.

Protanthium. The genome sizes among the diploid accessions ranged from 3.687 to 6.412 pg while high intraspecific variation in genome size was observed with up to 19.4%. Two species included accessions with different ploidy levels: K. rotunda L. (diploid, triploid and tetraploid) and K. takensis Boonma & Seansouk (diploid and tetraploid).

The increase in genome size of tetraploid K. rotunda is nearly in correlation to the increase in ploidy level, whereas the triploid plants represent genome expansion with an approximately 11% larger than expected genome. Interestingly, tetraploid K. takensis displays genome downsizing of 15.3% compared to their diploids. The cytogenetic characteristics, together with morphology, unequivocally clarify the taxonomic status of a new species, named Kaempferia calcicola Noppornch.

A revised identification key to species of K. subg. Protanthium is provided.