Two species of invasive goldenrods, Solidago canadensis and Solidago gigantea, are spread over all territories of Lithuania. Solidago × niederederi, a putative hybrid between S. canadensis and native Solidago virgaurea, was found in 27 populations mixed with the parental species. This research represents the characterization of S. × niederederi in comparison to the other mentioned Solidago species, with the use of one-way analysis of variance (ANOVA), principal-components analysis (PCA), and discriminant analysis of a large data set. Twenty quantitative, four qualitative, and five ratio morphological and anatomical characteristics, pollen viability, and somatic chromosome numbers of the four Solidago species were studied with the aim to ascertain inter- and intraspecific variation and reliable features identifying S. × niederederi, and to test the hypothesized hybrid origin. The PCA of morphological and anatomical characteristics showed the clear intermediate position of S. × niederederi compared to S. canadensis and S. virgaurea. The results showed that the most informative characteristics for the distinction of hybrids from parental species are floral traits such as the lengths of the disc, ray florets, and involucre. The intermediate stomatal characteristics and sharply decreased pollen viability discovered herein could potentially be used as an additional discriminating character in Solidago hybrid identification and support the hybrid origin of S. × niederederi.

Nomenclature: Goldenrods, Solidago × niederederi, Solidago canadensis, Solidago virgaurea.