Typhonium boonkerdii (Araceae), a Distinctive New Geophytic Species from Northeastern Thailand

Botanical exploration of northeastern Thailand has revealed substantial undocumented diversity within Typhonium (Araceae). Here, T. boonkerdii Chatan & Promprom is described and illustrated as a new geophytic species from Mukdahan Province. The taxonomic treatment is based on study of living plants during vegetative, flowering, and fruiting stages, together with comparative examination of herbarium specimens and relevant taxonomic literature. Typhonium boonkerdii is morphologically most similar to T. cucullatum but is distinguished by its shortly acute to shortly acuminate leaf-blade apex, longer and broader pistillate zone comprising 4-5 rows of densely congested pistils, larger ovaries and stigmas, broader sterile interstice, and mutually distant staminodes with downward- to slightly downward-directed apices. The new species further differs in having a longer staminate zone with 6-7 whorls of stamens, an appendix with an abruptly but slightly expanded base, and a longer stipe. Although both species show a similar sequence of spathe-limb movement during anthesis, the consistent combination of characters clearly supports the recognition of T. boonkerdii as a distinct species. The species is currently known from a single population in mixed deciduous forest at 300-400 m elevation. As the total population is estimated to comprise fewer than 50 mature individuals, the species is provisionally assessed as Critically Endangered (CR) following the IUCN Red List Categories and Criteria. A detailed description, photographic illustrations, distribution map, morphological comparison, and identification key are provided.