An Overlooked Tree Species, Micromeles Calocarpa (Rehder) M. Aizawa (Rosaceae), From Central Japan

In Japan, two simple-leaved species of trees of Rosaceae tribe Maleae have been treated as Sorbus alnifolia and S. japonica or have been assigned to the genus Aria. However, they are morphologically distinct from Aria and Sorbus and should be treated as species of Micromeles. Under S. japonica, variety calocarpa (hereafter only calocarpa) was described based on specimens collected in Nikko, Japan, where calocarpa is commonly found. Although calocarpa has been neglected, it is hypothesized that it should be treated as a distinct species characterized by larger leaves with a dense white persistently tomentose abaxial surface and round to truncate leaf base. The phylogenetic position of the Japanese simple-leaved species, including calocarpa, in the tribe Maleae was examined using chloroplast (cp) DNA regions. CpDNA analyses demonstrated that the Japanese taxa should be assigned to Micromeles. Second, to test the hypothesis that calocarpa should be recognized as a distinct species, its phylogenetic relationships among Japanese Micromeles using cpDNA and nuclear low-copy-number genes was examined. Leaf morphology of the three taxa was also compared. The phylogenetic and morphological analyses indicated that calocarpa is indeed distinct from M. japonica and M. alnifolia. Therefore, a new status and new combination, Micromeles calocarpa (Rehder) M. Aizawa, is proposed.