Morphological and Phenetic Evidence Support the Recognition of a New Limestone-Dwelling Species of Boesenbergia Kuntze (Zingiberaceae) from Northeastern Thailand

Limestone habitats in Southeast Asia often harbour narrowly distributed plant diversity, and several limestone-associated taxa of Boesenbergia require further taxonomic documentation. Field surveys and ex situ observations of living material from Loei Province, northeastern Thailand, revealed a distinctive Boesenbergia population associated with shaded limestone microhabitats. This study evaluates this population using comparative morphology, herbarium and literature comparisons, phenetic analyses based on 25 selected morphological characters, and a preliminary conservation assessment. Boesenbergia lamudiae Boonma, Saensouk & P.Saensouk, sp. nov., is described and illustrated. The species is morphologically most similar to B. burmanica Boonma, P.Saensouk & Saensouk, and resembles B. rotunda sensu lato in having a terminal inflorescence enclosed within the leaf sheaths and lacking an androecial cup. It differs by its broadly elliptic to ovate-elliptic laminae with an arachnoid abaxial surface, maroon lanceolate bracts, longer pubescent calyx with an acute to acuminate apex, non-saccate obovate labellum with a sharply delimited maroon transverse colour zone, larger anther crest, longer epigynous glands, and pubescent ovary. Principal coordinates analysis (PCoA) and unweighted pair group method with arithmetic mean (UPGMA) clustering based on Gower distance separated B. lamudiae from all compared operational units, supporting its morphological distinctiveness. The species is currently known only from Nong Hin District and is provisionally assessed as Critically Endangered (CR) under criterion D.