Low Genetic Diversity in the Highly Morphologically Diverse Sida fallax Walp. (Malvaceae) Throughout the Pacific

Abstract: Sida fallax Walp. (‘ilima) (Malveae, Malvoideae, Malvaceae) is native to the Pacific area and is broadly distributed throughout this region. Sida fallax is the most widespread and variable taxon of Malvaceae in the Hawaiian Islands and it occurs with diverse morphological forms and in different habitats from Hawai‘i Island to Midway Atoll. The low elevation and mountain ecotypes are two extreme ecological forms of S. fallax with many intermediate morphological types existing between these extreme ecotypes in the Hawaiian Islands. The range of morphological and ecological diversity in Sida fallax suggests that this species requires further biosystematics investigation. The purpose of this study was two-fold. First, explore the genetic diversity among S. fallax populations throughout its native range in the Pacific region to assess if it is a single species or potentially multiple cryptic species; second, investigate the biogeographic origin of S. fallax. To do this, Sida fallax was sampled throughout the Hawaiian Islands and in different parts of the Pacific region. Bayesian phylogenetic analyses based on nuclear (ITS and ETS) and chloroplast regions (psbA–trnH) were carried out. Results indicate that there is very little sequence-level variation in this species throughout its distribution and phylogenetic analysis clearly demonstrated that Sida fallax is a single species throughout the Pacific region and the different forms of Hawaiian S. fallax are not genetically distinct at the sequence level. Although the pattern of dispersal of S. fallax is not clear, an American origin is most likely.