A New Species of Pycnospatha (Araceae) from Eastern Thailand, with an Updated Key to All Known Species

Pycnospatha is a small and poorly known genus of Araceae distributed in Indochina and currently comprising only two accepted species. During botanical surveys in Si Sa Ket Province, eastern Thailand, an unusual population of Pycnospatha was discovered in a dry dipterocarp forest and found to differ from both P. arietina and P. palmata. Here, we describe this plant as a new species, Pycnospatha phanomdongrakensis. The new species is distinguished by a combination of characters, including a slender habit, shorter petiole and peduncle, a medium-sized spathe, a short and dense spadix, a distinctly curved style directed toward the apex of the spadix, a geophilous and ovoid infructescence, obovate berries, and asymmetrically ovoid seeds. The new taxon is currently known only from a single population in the Phanom Dong Rak mountain range. A preliminary conservation assessment is provided, and the species is treated as Critically Endangered (CR) following IUCN guidelines. An identification key to all species of Pycnospatha is also presented. The discovery of this new species highlights the continuing importance of field-based taxonomy in revealing overlooked aroid diversity in the seasonally dry forests of eastern Thailand.