Arisaema nonghinense (Araceae), a new species from Thailand

Recently, the volume on Acoraceae & Araceae has been published in the Flora of Thailand and among the numerous genera of Araceae, the genus Arisaema Mart. is one of the largest, with c. 200 species (Gusman & Gusman 2006; Li et al. 2010), primarily in warm temperate or subtropical regions. In Thailand, 18 species, 3 subspecies and 1 variety were recorded, of which 8 species are endemic (Gusman 2012). During a field trip to a limestone hill in Nong Hin district, Loei province, northeastern Thailand, a species of Arisaema was discovered that matched none of those accounted for in the Flora of Thailand. A. nonghinense is member of section Fimbriata because it has a deciduous habit, a subglobose subterranean tuberous stem, a conspicuous pseudostem and one or two trifoliolate leaves whose leaflets are petiolulate. Like all members of this section, about 20 from tropical and subtropical SE Asia, the spadix appendage is sessile and subulate, with sterile flowers above the fertile part at least in female spadices. The closest species in the section, is A. fimbriatum Mast. (Masters 1884), growing in south Thailand and Malaysia, with which it shares a very long, branching spadix appendage whose apical part is covered with long and flexuous filaments. Such very long branching spadix appendages are present in other species such as A. victoriae V. D. Nguyen (Nguyen 2000), A. tsangpoense J. T. Yin & Gusman (Yin & Gusman 2006). However, these two taxa are members of the section Anomala Gusman & L. Gusman (in Hetterscheid & Gusman 2003) because they are rhizomatous and evergreen, hence easily distinguished from section Fimbriata. The pale yellow colour of the spathe is also uncommon for the genus. This new Arisaema species occurs in humus rich soil in moist limestone rock crevices in semishaded areas, and is probably endemic to the limestone ranges of Loei province, NE Thailand.