The systematic study of Taiwanese Arisaema (Araceae)

The genus Arisaema (Araceae) in Taiwan is revised based on comparative morphological, palynological, and cytotaxonomical studies. Nine species and one variety, including two new taxa (A. ilanense J. C. Wang sp. nov. and A. thunbergii ssp. autumnale J. C. Wang, J. Murata & Ohashi ssp. nov.), are recognized. By the re-collection of fresh materials and a detailed comparison, A. matsudai Hayata, which was previously reduced to synonymy under A. grapsospadix Hayata, is now treated as distinct. Rhizome shape, arrangement of leaflets, ratio of pseudostem to petiole length, and spadix-appendage morphology are all important characters in separating the Taiwanese taxa. Pollen morphology also displays interspecific variation in size, spinule length, and spinule density. Cytologically, all examined species have 28 chromosomes (diploid), but three of them are also found to have 56 chromosomes (tetraploid). The chromosome numbers 2n=28 of A. ilanense and A. thunbergii ssp. autumnale, and 2n=56 of A. formosanum and A. heterophyllum are determined for the first time. A key to the taxa along with descriptions, illustrations, distribution maps, and taxonomic notes are provided.