Permalink : http://hdl.handle.net/2115/34834

The genus Acer is commonly known in the Tertiary of the Northern Hemisphere, represented by leaves (or leaflets) and winged seeds. However, these fossil leaves have been frequently difficult to determine their modern relationships only by gross features. In order to compare accurately the fossils with the extant species, the vein system of 117 living species of the genus Acer have been examined by the cleared leaf method. Based on areolation and minor venation characters, all the species in the world are classified into two groups. In the first group the ultimate veinlets ramify more than twice within the areoles, once branching, while in the second group the freely-ending veinlets are mostly lacking or single, and rarely once branching. The taxonomic system of the genus Acer has been proposed by various authors, since Pax (1885-1886) first published the detailed systematics. Compared with these systems, the above-noted classification by the venation characters are well consistent with the system described by Ogata (1967), excepting a few species. Following to Ogata's system, the venation characters of the genus Acer are briefly described with the illustrations.