Natural and human drivers both drive novel assemblages of native and non-native plants in urban vegetation, but they are often studied separately. We studied both planted and spontaneously-established plants in urban parks to understand how natural and human drivers co-determine urban plant assemblages. Vascular plants in 78 Taipei City parks covering 336.6 ha were surveyed through a complete sweep of all vegetation. Park typologies were defined using nonmetric multidimensional scaling of 1149 species and park characteristics. NMS1 was defined by planted species and was most related to park-size: Small community-parks had a low diversity of shade-trees and small shrubs/ornamental-plants; Large multifunctional parks had the highest plant diversity. NMS2 was defined by spontaneously-established species and determined by vertical structure: Natural forest remnants were structurally the most complex, hosted many spontaneously-established native shruband epiphyte-layer species, and had the highest native diversity; City beautification parks had the simplest structure and low planted diversity, but hosted a high richness of spontaneously-established herbaceous plants, many of them non-natives. Alternative "anthropogenic versions" of various species-area hypotheses were proposed. Although landscape designers are the dominant drivers of plant composition in urban parks, the variety of artificially-created habitat structures provided the settings upon which natural ecological processes of spontaneous establishment could unfold. Landscape architects could enhance native species persistence by providing a diversity of habitat structures, using natural elements and a higher abundance of native herbaceous species, and ensuring potential habitats for native herbaceous and epiphyte species in urban greenspaces are effectively connected to their natural populations.
