This study was intended to identify 17 taxa. (5 varieties and 12 species) of the genus Acer in Korea on the basis of the shapes of stomata, the type of trichome on the different part of leaves, the shapes, arrangement and number of stele in cross section of petiole. The results obtained were summarized as follows; 11 The shape of guard cells of stomata in the genus Acer was anomcytical, and the size of the cells ranged from 10.25 to 21.00 μ in length and from 7.57 to 11.83 μ in width. 2) Eleven types of trichome on the leaf in the genus Acer were found; pilose, sericeous, velutinous, woolly, glabrate, puberulent, bladder hair, hispid, hirsute and uncinate. This characteristics also established a good criterion for identification of species. 3) The stele of petiole in the genus Acer was characterized by eustele and atactostele with polybranch, and the six groups of the shape of numerical change of stele; B$gt;M=T, B$lt;M=T, B=M=T, B$gt;M$lt;T, B$lt;M$lt;T, B=M$lt;T were found at Three parts of petiole, where, B : the number of ramified stele at the base part of petiole, M : the number of ramified stele at the middle part of petiole, T : the number of ramified stele at the terminal part of petiole. 4) The shapes of petiole in cross section of the genus Acer were a, b, c, d, e, f and g shape. The $quot;b$quot; shape appeared in 7 species and had the hightest appearance frequency. The $quot;a$quot; and $quot;c$quot; shape appeared both in 4 species. The $quot;g$quot; shape appeared in 3 species. And the $quot;d$quot;, $quot;e$quot; and $quot;f$quot; shape appeared in 2 species. In conclusion, it was possible to identify 17 taxa. of the genus Acer in Korea by the shape of stomata, trichome and the shape, arrangement, and number of stele in cross section at three parts of petiole.