Recurrent occurrence of <i>Linaria simplex</i> (Plantaginaceae) on railway ballast: A new alien plant record for Korea

<i>Linaria simplex</i> Desf. (Plantaginaceae), an alien species not previously recorded in Korea, is reported from railway ballast near Sinseondae Station in Busan. The species was repeatedly observed and collected at the same railway-associated locality in 2022, 2023, and 2026. In Korea, two species of <i>Linaria, L. japonica</i> Miq. and <i>L. vulgaris</i> Mill., and several morphologically similar alien taxa of the tribe Antirrhineae, including <i>Nuttallanthus canadensis</i> (L.) D. A. Sutton, <i>Chaenorhinum minus</i> (L.) Lange, and <i>Kickxia elatine</i> (L.) Dumort., have been reported. <i>Linaria simplex</i> is distinguished from the Korean species of <i>Linaria</i> and from morphologically similar alien Antirrhineae taxa by its annual habit, lower leaves often whorled, small pale yellow corollas with mauve veins, short, straight, downward- directed spurs, and compressed discoid seeds with a broad marginal wing. This railway- ballast population appears to be locally persistent in a dry, open, and repeatedly disturbed transport-associated habitat, although its naturalization status requires further evaluation. We provide a morphological description, distributional information, voucher specimens, photographs, scanning electron micrographs of seeds, and a taxonomic key to the species of <i>Linaria</i> recorded in Korea.