A deciduous tree 40 to 80 ft high in the wild, with a grey-barked trunk 1 to 3 ft in diameter; young shoots glabrous or sparsely hairy. Leaves of firm texture, roundish ovate, sometimes almost kidney-shaped, coarsely toothed, rounded or shortly pointed, heart-shaped at the base, 2 to 31⁄2 in. long, usually as wide or even wider than long, glabrous except for tufts of pale down in the vein-axils; stalk 1 to 11⁄2 in. long. Flowers 1⁄2 in. wide, numerous on the cyme, borne on slender stalks, the bract 11⁄2 to 21⁄2 in. long, 1⁄2 in. or more wide, not downy. The whole inflorescence is 3 to 4 in. long; fruits obovoid, 3⁄16in. long.
Native of Korea on Daghelet Island (Cheju Do), whence it was introduced by Wilson in 1919. It is allied to T. cordata and flowers at about the same time, differing in the coarser acuminately tipped teeth, sometimes enlarged into a lobule when terminating a main lateral nerve, in the regular presence of staminodes in the flowers, and in the long-stalked pendulous inflorescences 2 to 3 in. across, with up to thirty-six flowers in each. A charming small tree, which deserves to be more widely planted. It is, however, uncommon in cultivation, the largest examples being: Kew, pl. 1928, 38 × 21⁄4 ft (1967); Edinburgh Botanic Garden, 33 × 21⁄2 ft (1970); Westonbirt, Glos., Pool, 50 × 21⁄2 ft (1970); Thorp Perrow, Yorks, 42 × 21⁄2 ft (1974).
T. insularis is scarcely more than a local race of the following, described earlier:
T. japonica (Miq.) Simonkai T. cordata var. japonica Miq. – As in the preceding, the inflorescences are many-flowered and pendulous, and the flowers have staminodes; the bracts are usually long-stalked. Leaves more or less orbicular in outline, not lobulate, up to 3 in. long, cordate. It is uncertain if the true species is in cultivation. A tree at Borde Hill, planted as T. japonica, has ovate leaves, mostly with a narrow lobule on one side, inflorescences with up to only ten flowers, not pendulous; bracts sessile or short-stalked. It is perhaps referable to T. amurensis Rupr., a native of Amurland, N. Korea, etc., and thus a near neighbour of T. japonica, which extends from Japan to E. China. The Borde Hill tree, whatever its correct name, is one of the most ornamental of the limes, with a conical, densely leafy crown, and flowering from almost every node in some years. The bright green young leaves appear early in the spring but are not damaged by frost. The tree was planted in about 1910 and measures 43 × 41⁄2 ft (1968).