Yi Zhou, School of Landscape Architecture , Beijing Forestry University, Ming Cai, Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, National Engineering Research Center for Floriculture and College of Landscape Architecture, Beijing Forestry University, Qixiang Zhang, Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding , National Engineering Research Center for Floriculture , Beijing Laboratory of Urban and Rural Ecological Environment and College of Landscape Architecture, Beijing For and Donglin Zhang, Universisty of Georgia