The morphological characters, pollen viability, and molecular markers are used in this study to assess the inter-species differentiation in Taiwan Trema( T. orientalis, T. tomentosa, T. cannabina, and the hybrid ). The hybrid was proposed to have been originated from T. tomentosa and T. cannabina natural hybridization with morphological, pollen viability and molecular marker evidences. The four taxa are variable in the following morphological characters: growth form, terminal bud color, leaf size, leaf apex, leaf base, leaf vestiture, leaf texture, leaf nerves, petiole, stipule size, inflorescence sex, male and female inflorescence length, flower number, mature fruit color, perianth vestiture, male flower perianth size, pistillode size, pistillode shape, filament length, and female flower size. The author also found differences in leaf shape, leaf size, leaf base, and leaf vestiture between adult and juvenile individuals of T. orientalis are ontogenetical variations. The hybrid is morphological intermediate between T. tomentosa and T. cannabina, possessing species-specific morphological characters of either species. Leaf trichome morphology was observed under scanning electronic microscope, and a unicellular trichome type with bulbous base, smooth surface, and creeping looking, is specific to T. orientalis leaf abaxial surface. In pollen viability tests, the hybrid had the lowest average pollen stainbility among tour taxa, but varied widely from 48.5 % to 81.6 %. In additivity test of molecular markers, for all 8 species-specific molecular markers of T. tomentosa, 6 were detected in hybrid; for all 14 species-specific molecular markers of T. cannabina, 11 were detected in hybrid; and none of 14 species-specific molecular markers of T. orientalis were detected in hybrid. Additionally, there were some recessive homozygote alleles detected in hybrid molecular marker, and even missing in T. tomentosa molecular markers. According to this evidence, there was a possible introgression between the hybrid and parental species-T. cannabina. In similarity dendrogram derived from molecular markers, all samples were clustered into four taxa-corresponded groups, the hybrid was placed between T. tomentosa and T. cannabina, and closely related to T. cannabina.