Let me show you 7 typical kinds of Acer mono (Acer pictum) in Japan here as follows.

Enkoh-kaede (f.dissectum), Taishaku-itaya (f.taishakuense), Urajiro-itaya (f.glaucum), Aka-itaya (f.mayrii), Ezo-itaya (f.mono), Oni-itaya (f.ambiguum) and Itomaki-itaya (f.savatieri).

From left to right, flowers of Oni-itaya (f.ambiguum),
Enkoh-kaede (f.dissectum) and Itomaki-itaya (f.savatieri)

Well, let me show you Enkoh-kaede (f.dissectum) that is seen near mountains not so high. The lobes of their leaves are not so wide and the image of the leaves look like monkey's hand, they are called Enkoh-kaede. Enkoh means monkey.

Another name of Acer mono ssp. marmoratum is Enkoh-kaede (f.dissectum).

Upper : Enkoh-kaede (f.dissectum) at Koishikawa Botanical Garden
Lower : Sprouting & Summer leaves of Enkoh-kaede (f.dissectum)

Secondly, let me show you Taishaku-itaya (f.taishakuense) and Urajiro-itaya (f.glaucum) whose leaves are similar to those of Enkoh-kaede (f.dissectum) in size and shape.

Taishaku-itaya (f.taishakuense) is only found on limestones of Taishaku-kyo Valley in Hiroshima Pref. in Japan.

Pilose along the main veins of the upper surface of Taishaku-itaya.
Pilose on the whole upper surface in this picture.

Leaves of Taishaku-itaya are also pilose on the whole lower surface and on the petiole.

Then, Urajiro-itaya (f.glaucum), which are distributed in Niigata, Yamagata and Fukushima Pref.

Leaves are somewhat thicher and are characterized by being glaucum beneath.

Left : Urajiro-itaya, Right : Aka-iataya

There are maples whose leaves are glaucous beneath, such as Acer pycnanthum in Japan, silver maple in North America, sycamore maple/ Montpellier maple/ Balkan-Ahorn in Europe, trident maple/ paperbark maple in China and Acer laurinum in the Southern Hemisphere and some others.

Some samples of maples whose leaves are glaucous beneath

Next, let me show you Aka-itaya (f.mayrii), Ezo-itaya (f.mono), Oni-itaya (f.ambiguum) and Itomaki-itaya (f.savatieri). These trees are large.
Aka-itaya (f.mayrii) is distributed in Hokkaido and Honshu, Ezo-itaya (f.mono) in Hokkaido and nothern Honshu, Oni-itaya (f.ambiguum) in almost all over Japan and Itomaki-itaya (f.savatieri) mainly limited to Central Honshu.

Upper left : Aka-itaya (f.mayrii), upper right : Ezo-itaya (f.mono)
Lower left : Oni-itaya (f.ambiguum), lower right : Itomaki-itaya (f.savatieri)

New leaves of Aka-itaya (f.mayrii) is remarkably reddish as the picture below shows. In spring it is easy for us to find Aka-itaya with yellow flowers in the forest. So, it was named Aka-itaya, and "aka" means "red".

Aka-itaya (f.mayrii) seen arround Mt. Moriyoshi in Akita Pref.

Leaves of Aka-itaya are wide and usually have 5 lobes.
Upper left : spring leaves, upper right : summer leaves, lower left : autumn leaves
Lower right : Yellow leaves arround Hohei-kyo Valley in Hokkaido

Spring leaves & summer leaves of Ezo-itaya (f.mono)

Next, let me show you Oni-itaya (f.ambiguum). Leaves of Oni-itaya (f.ambiguum) are peculiarly covered with short hairs all over the underside. So, we can easily identify oni-itaya by finger feeling of the hairs. The following picture shows that the hairs can be obserbed by scanning of folding leaf with black paper for a background.

Oni-itaya (f.ambiguum) has short hairs all over the underside.

Shape of a leaf & autumn color of Oni-itaya (f.ambiguum)

Oni-itaya at Taishaku Valley(upper left), Mosakubo(upper right), Kyoto and Hamamatsu

Upper left : Oni-itaya (f.ambiguum), upper middle : Itomaki-itaya (f.savatieri) upper right : Aka-itaya (f.mayrii)
Lower left : Enkoh-kaede (f.dissectum), lower middle : Ezo-itaya (f.mono), lower rightAka-itaya (f.mayrii)

Lastly, let me show you 4 pictures of basal axils on the under surface and the apex of the petioles for comparison.

Upper left : Oni-itaya ; Hairs on petioles & main veins, short hairs all over the underside
Upper right : Itomaki-itaya ; Thick brown-villose on the basal axils &the apex of the petioles
Lower left : Ezo-itaya (f.mono) ; pubescent with the base of the petioles of leaves
Lower right : Aka-itaya ; glabrous beneath except the base of main veins and the apex of the petioles