Anatomical characters (e.g. leaf, stem, main vain of leaf, length of pallisade parenchyma, leaf epidermis, and rostrum in fruit) on 35 species of Geranium in Asia were investigated. Based on the degree of stem rib-angle development, the genus divided into two subgenera. Subgenus Geranium had developed stem rib-angle while subgenus Robertium has undeveloped one. Cortex parenchyma of petiole in subgenera Geranium and Robertium consisted of six to nine and three to five layers, respectively. The length of pallisade parenchyma was one of the most important characters for the classification of two subgenera. Pallisade parenchymas of subgenus Geranium were elongated as half as mesophyll cells, however, those of subgenus Robertium were shorter than the half length of mesophyll cells. Each central columella was one layered parenchyma in subgenus Robertium and section Tuberosa of subgenus Geranium, while two layered parenchyma were observed in section Geranium of subgenus Geranium. The genus of Geranium in Asia were classified into two subgenera on the characters such as the degree of stem rib-angle development, the number of cortex parenchyma layer, and the length of pallisade parenchyma. The central columella of rostrum was one of the most useful taxonomic character to classify the subagenera and sections. The results showed that subgenus Geranium was more advanced than subgenus Robertium. This study suggested that the infrageneric system proposed by Yeo, was approved for the taxonomic study of Geranium in Asia
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