Abstract Current phylogenetic studies indicate that the genus Sibbaldia is a paraphyletic group, which has been taxonomically divided into three distinct smaller genera distributed across different lineages within the tribe Potentilleae. Given that, within the Potentilleae, the traditionally defined genus Sibbaldia exhibits a distinct morphological trait—typically possessing only a single whorl of stamens—that distinguishes it from other related genera that have more than one whorl of stamens. Understanding the current phylogenetic classification requires an investigation into the developmental patterns of stamen reduction across different lineages of Potentilleae. A floral developmental investigation of four species, most of which used to belong to the genus Sibbaldia, was carried out using scanning electron microscopy, combined with character optimization of stamen number in Potentilleae. The results indicated that, in the tribe Potentilleae, the ancestral state of the androecium consists of 20 stamens arranged in three whorls. Androecium developmental patterns in Chamaerhodos, Sibbaldia sensu stricto, and Sibbaldianthe are consistent with that displayed by their mature structures. However, the developmental processes giving rise to single-whorled androecia in these three genera show no phylogenetic correlation. Instead, they each imply the involvement of different whorls of the ancestral stamen developmental pattern of Potentilleae. In different genera, the specific whorl of stamens that is lost appears to be influenced by spatial constraints within the floral meristem. These results also provide strong morphological support for the current molecular phylogeny of the genus Sibbaldia.
Wei et al. (Fri,) studied this question.