Aster xuelinii (Astereae, Asteraceae), a new species growing on moist rocks from Gansu Province, China

<i>Aster xuelinii</i>, a new species from Gansu Province, China, is described and illustrated based on morphological and phylogenetic evidence. The new species is superficially similar to <i>A. dolichopodus</i> Y. Ling in that both have nearly entire leaves, synflorescence solitary at branch tips or arranged in corymbiform clusters, and ray floret color. However, it differs from <i>A. dolichopodus</i> in having peduncles 6-9 cm in length and 12-14 ray florets, versus 2.5-15 cm in length and 19-26 ray florets. Phylogenetic analyses of nuclear ribosomal ITS and ETS sequences, as well as the chloroplast <i>trnL-F</i> region, place this new species within the genus <i>Aster</i>, where it forms a well-supported clade with <i>A. taliangshanensis</i> Y. Ling. <i>A. xuelinii</i> differs from <i>A. taliangshanensis</i> in that the latter has stems often purplish-red in the upper part, capitula typically arranged 1-3 at branch tips forming a loosely corymbiform synflorescence, and a higher number of ray florets (50-60), which are bluish-purple. Furthermore, detailed morphological descriptions, diagnostic illustrations, and ecological habitat characteristics are provided, supporting the classification of this new species.