| Syringa L., a genus of the family Oleaceae, is distributed in the southeastern Europe and East Asia westwards to the Himalayas. China is the modern distribution centre of the genus. 16 native species of Syringa were recorded in the Flora Reipublicae Popularis Sinicae (Vol. 61,1992) and in the Flora of China (Vol. 15, 1996), but the taxonomic treatment was slightly different between them. There have been some controversial views on the infrageneric and specific delimitation. Species such as S. persica L. and S. sweginzowii Koehne et Lingelsh. were described from the cultivated plants and no type specimens were designated for them. This caused the difficulty in the taxonomy of this genus. The variation pattern of the characters is very complicated. It is hard to make a reliable taxonomic treatment based on limited herbarium specimens. Extensive literature survey and specimen examination were conducted, and population sampling and field observation were made in this study. Character variations within and between the populations were analyzed statistically in order to evaluate the taxonomic significance of the characters. Hence a taxonomic revision of the genus is made on the basis of character analysis in the present work.More than 2000 specimens from 16 herbaria were examined, including ca. 70 type specimens. More than 40 populations were sampled in 12 provinces and regions of China, and over 500 specimens were collected and observed in the field, covering most taxa recorded in the Flora Reipublicae Popularis Sinicae (Vol. 61) except S. tibetica P. Y. Bai. Variations of more than 40 characters within and between populations of nine species complexes were statistically analyzed. The results show that characters such as the type of leaf division, length of petioles, type of inflorescences, size of corollas, length of filaments and color of anthers were distinct among the taxa, which can be used in the species circumscription. Characters such as the shape of leaf blades, indumentum on leaf blades and inflorescence raches and shape of corolla tubes varied continuously among populations of some species complexes, which can only be used for infraspecific delimitation. Characters such as the size of leaf blades, shape of inflorescence raches, position of anthers inserted on the corollas and coverage of lenticels on capsules varied discontinuously or continuously among the populations of different species complexes, which can be employed for specific or infraspecific delimitation, or just considered as variation within taxa. Characters including the venation pattern of leaf blades, color of corollas, shape of calyx lobes and corolla lobes were scarcely different among populations, which have little taxonomic significance.On the basis of character analysis and multivariate analysis, 12 species and 13 subspecies (in 2 sections and 2 series) of Syringa are recognized in this article. Sect. Ligustrina comprises 1 species and 3 subspecies, and sect. Syringa includes ser. Villosae (5 species and 5 subspecies) and ser. Syringa (6 species and 5 subspecies). The types are designated for each section and series, and the keys to sections, series, species and subspecies are made. Each species and subspecies is morphologically described, with examined specimens cited, distribution map provided, and views on taxonomic treatment proposed. Four new combinations were proposed: S. meyeri C. K. Schneid. was reduced to a cultivar, S. pubescens'Meyer', S. wolfii C. K. Schneid. to S. villosa subsp. wolfii, S. sweginzowii Koehne et Lingelsh. to S. yunnanensis subsp. sweginzowii , and S. tomentella Bureau et Franch. to S. yunnanensis subsp. tomentella. Eleven botanic names are treated as synonyms, i.e., S. fauriei H. Lév., S. julianae C. K. Schneid., S. meyeri var. spontanea M. C. Chang, S. pinetorum W. W. Sm., S. wardii W. W. Sm., S. oblata var. donaldii R. B. Clark et J. L. Fiala, S. afghanica C. K. Schneid., S. protolaciniata P. S. Green et M. C. Chang, S. tibetica P. Y. Bai, S. reflexa C. K. Schneid. and S. wilsonii C. K. Schneid. The lectotypes of 3 species and 4 subspecies are designated, i.e. S. reticulata subsp. reticulata and subsp. amurensis, S. pubescens subsp. microphylla and S. oblata subsp. dilatata. Lectotypification of other 10 taxa is also made. The principles for the taxonomic treatment are proposed. The records of Syringa species in local florae of China are reviewed and the global distribution pattern of the genus was discussed.Observations on chromosomes of 16 accessions of 13 taxa of Syringa were conducted. The results show the chromosomal number of all taxa is 2n=46 except S. yunnanenis subsp. tomentella, which is 2n=48. The chromosomal number of S. oblata subsp. dilatata is reported for the first time. Chromosomes of S. pubescens subsp. microphylla, S. meyeri'Palibin'and the hybrid between S. pubescens subsp. microphylla and S. meyeri var. spontanea were also observed and no significant difference was detected, which supports the taxonomic treatment in this article. In addition, the chromosomal number was scarcely different between the materials from wild S. persica (S. protolaciniata) and that from cultivated plants.
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