Morphology and phylogenetic relationships of thirteen cultivars of ~iDimocarpus longan~i and five others genera of Sapindaceae from Thailand were investigated. Some characters are distinct between cultivars and can be used as tools in identification. Some characters are continuous and cannot be used as the tools. The fruits or leaves are the major characters to be used as a tool in identification longan cultivars. Cluster analyses using the unweighted pair-group method with arithmetic average (LTPGMA) divided thirteen cultivars of ~iDimocarpus~i species into four groups on a hundred and one morphological and ecological characters. Thirteen cultivars of ~iDimocarpus longan~i. Thai longan is separate into three groups

early-maturing mid-maturing and late-maturing. The other genera of Sapindaceae

Litchi species, ~iNephelium~i species

~iXerospermun~i species, ~iSchleichera~i species and ~iLepisanthes~i species were clustered separately from Dimocarpus species. The phylogenetic relationships at interspecific level of four subspecies (subsp. fumatus, subsp. indochinensis, subsp. malesiarrus and subsp. longan), thirty=six cultivars of Dimocarpus longan and four other related genera collected in Thailand were examined. They could be divided into Dimocarpus species two distinct groups

Dimocarpus fumatus and Dimocarpus longan. Litchi species was the closest relative with Nephelium species. Xerospermum noronhianum and Lepisanthes rubiginosa showed farther distance from Dimocarpus species. The results indicated Dimocarpus, species showed most close relationship with Litchi species and Nephelium species. The phylogeneticrelationships at intraspecif c among twenty-five cultivars of Dimocarpus longan were analyzed by comparing 357 AFLP markers. They could be divided into Dimocarpus longan three distinct groups

Thai, Vietnamese and Taiwanese cultivars. Dimocarpus species is more closely to Litchi species than Xerospermun, Lepisanthes and Nephelium species. RFLP analysis was suitable for classification among species. However, AFLP markers could be rapidly used for study of the phylogenetic relationship among cultivars especially for ~iDimocarpus~i spp.