Abstract
In 2008, we investigated the bark surface structure and resin duct index (RDI) in cross-section of needles of Japanese black pine (Pinus thunbergii Parl.) trees growing in Okinoshima-cho, Shimane prefecture, Japan, in relation to the hybridity of this species. In most of the sampled trees, called Ai-guro pines, the bark surface had hybrid-like characteristics, between those of the Japanese black pine and the Japanese red pine (P. densiflora Sieb. et Zucc.). However, the RDI values of all the sampled trees corresponded to those of the Japanese black pine. Therefore, on the basis of the RDI values, we considered that pine trees classified as Ai-guro pines in Okinoshima-cho are not hybrids but in fact Japanese black pines.
