Notes on Allium section Rhizirideum (Amaryllidaceae) in South Korea and northeastern China: with a new species from Ulleungdo Island.

Allium section Rhizirideum is reviewed for South Korea and neighboring northeastern China based on critical observation of wild populations and herbarium materials. Species delimitations are re-evaluated on the basis of morphological and somatic chromosome numbers, resulting in the recognition of five species. Allium dumebuchum from Ulleungdo Island, South Korea, is described as a new species. This species is most similar to A. senescens due to its habits, but is clearly distinguished particularly by its rhomboid scapes in cross-secion, light purple perianth color, entire and narrowly triangular inner filaments, and flowering season from late September. One previously recognized species is placed into synonymy: A. pseudosenescens (under A. senescens). Photographs and a key to species of Allium section Rhizirideum in South Korea and northeastern China are provided in addition to information on nomenclatural types, synonymies, chromosome numbers, distribution, and specimens examined.