Several additional of Forsythia are grown and may escape, including F. viridissima, the green-stemmed Forsythia, with pith chambered throughout and simple leaves, and F. ovata, the early or Korean Forsythia, with stiffly upright twigs and ovate leaves. Many cultivars are also grown.
All species found in Forsythia
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. January 28, 2020. https://michiganflora.net/genus.aspx?id=Forsythia.