Fortunella Swingle belongs to Rutaceae, which is an evergreen shrub or small tree, distributed in Southeast Asia. China is the most abundant country in the distribution of the genus, and all the species of the genus are concentrated in China. The plants of this genus are unique fruit resources in China, almost all species are rare in the wild and are rare and endangered plants, and the protection and classification of its resources have been concerned. The lack of knowledge of the key taxonomic characteristics and the different understandings of the species scale has led to a long-term controversy on its systematic status and taxonomy.

In order to clarify the systematic status of Fortunella and the taxonomic relationship under the genus, the East African Flora and Taxonomy Group of Wuhan Botanical Garden, cooperated with researchers from Hunan Normal University and the Rural Workstation of Hunan Eco-environment, carried out a large number of field investigations in China for Fortunella plants, and the first-hand detailed and accurate morphological data of the genus were obtained. The pollen characteristics were observed by scanning electron microscope, and the pollen micromorphological data of Fortunella were obtained.

Researchers have sampled extensively throughout the country, constructed the phylogenetic relationship of the genus by using the chloroplast genome and ITS fragments, confirmed the key characteristics of the classification of Fortunella, revised the classification of Fortunella, and solved the problems of the system status and subgenus classification of Fortunella.

The results reveal that according to the morphological, palynological, and molecular biological evidences, Fortunella and Citrus are closely related, and there are overlaps in morphology and palynological and molecular biological characteristics. This study supports the inclusion of Fortunella into Citrus. The morphological and palynological characteristics of F. venosa, F. hindsii, and F. japonica are different, and the three species should be considered as independent species. F. swinglei, F. margarita, F. bawangica, and several hybrids have no essential differences from Fortunella and are treated as synonyms of the latter respectively.

In this study, F. venosa and F. hindsii are transferred to Citrus as independent species, and new combined names for these two species are proposed. Their species names still use the previous species epithets:
(1) Citrus venosa (Champ. ex Benth.) K.M. Liu, X.Z. Cai & G.W. Hu, comb. nov.
(2) Citrus hindsii (Champ. ex Benth.) K.M. Liu, G.W. Hu & X.Z. Cai, comb. nov.

Citrus japonica Thunb. was originally placed in the genus Citrus when it was first named by Thunberg in 1780, and its scientific name should be restored.

The research paper entitled “Fortunella venosa (Champ. ex Benth.) C. C. Huang and F. hindsii (Champ. ex Benth.) Swingle as Independent Species: Evidence From Morphology and Molecular Systematics and Taxonomic Revision of Fortunella (Rutaceae)” was recently published in the international botanical journal Frontiers in Plant Science.

This study was supported by National Science and Technology Fundamental Resources Investigation Program of China; Investigation of Forest Tree Germplasm Resources in Hunan Province; Compilation of Rural Biosafety Planning in Hunan Province.

 Distribution of Fortunella (Image by WANG Ting)

Comparison of morphological characteristics of Fortunella. A. F. japonica B. F. venosa C. F. hindsii (Image by WANG Ting)
 

Gene map of Fortunella chloroplast genome (Image by WANG Ting)

Phylogenetic analysis of Fortunella and related taxa (Image by WANG Ting)