A New Species of Curcuma subgen. Ecomatae (Zingiberaceae) from Southwestern Thailand: Morphological Delimitation and Phenetic Evidence

Curcuma subgen. Ecomatae comprises several morphologically similar taxa whose delimitation requires careful evaluation of character combinations and intraspecific variation. Botanical surveys across Southwestern Thailand revealed six geographically separated populations of an unidentified Curcuma in Uthai Thani, Kanchanaburi, Ratchaburi, Phetchaburi, and Prachuap Khiri Khan provinces. Taxonomic status was evaluated through detailed comparative morphology and complementary individual-level phenetic analyses of 42 morphological characters using Gower distances, UPGMA clustering, and principal coordinates analysis (PCoA). The analyses comprised a population-level assessment of 120 individuals from six populations and an interspecific comparison of 200 individuals, including the same 120 individuals of the putative new taxon and 20 individuals each of four morphologically allied species. The populations are recognized here as a distinct species, Curcuma tenasserimensis Boonma, Saensouk & P.Saensouk, sp. nov., based on a consistent combination of vegetative, inflorescence, floral, and reproductive characters that distinguishes them from the morphologically allied species examined. The population-level analysis revealed morphological variation among the six geographically separated populations while retaining their overall morphological cohesion. In the interspecific analysis, individuals of C. tenasserimensis formed an overall morphologically cohesive assemblage that was differentiated from the four allied species examined. Together, comparative morphology and individual-level phenetic analyses are consistent with the recognition of C. tenasserimensis as a morphologically distinct species and further document the still-emerging diversity of subgen. Ecomatae in Southwestern Thailand.