Japonicum always have reliable fall colors, rarely show any Summer stress, and are less prone to frost in early Spring and stand up better to cold during fall show. They also have better disease resistance and drought resistance. They are less prone to powdery mildew in extreme heat and humidity of July and August. More cold hardy in our extremely cold and windy winters. I still love them both! Despite some of the challenges of palmatum you can't live without the diversity of all the different cultivars! They are a labor of love that are so rewarding when you treat them right! With that said, every garden needs at least a few japonicum cultivars!
Japonicum is much harder to grow from seed than palmatum. Young seedling have a tendency to die for no apparent reason, like the roots are sensitive to water molds or lack of oxygen maybe.
Very interesting comments! Another question is whether you can tell Acer japonicum apart from A. palmatum just by looking at them.
A common name for Acer japonicum is downy Japanese maple. A. japonicum are hairier on the leaf undersides and stems.
japonicum have subsp. like palmatum? again, japonicum is native to hill or mountain? next september I make a conference on Japanese maples and I want to be well prepared with the helpvs, not the first one I do but this is in the botanical garden (Lucca) and the public will be an expert :-)
I can't answer your question about subspecies, but there are two Botany Photo of the Day entries on Acer japonicum. Note the comments in both. Acer japonicum ‘Aconitifolium’ Acer japonicum ‘O-taki’
So Alex, obviously you've got to dip into the reference books which I know you own! :) In spite of Doug's desire to make a "dissectum group" for japonicum, there are no such groups recognized, unlike the various groupings given to palmatum and subspecies. (You will find Cor's latest such classification, which is accepted by the Maple Society, in the Symposium Proceedings. Once I get my act together I will publish an abbreviated version here and elsewhere). A. japonicum has larger leaves than palmatum, 8-15 cm and 7-11 lobed. A. palmatum has 5-7 lobed leaves that are 5-10 cm. Careful: frequent hybridization with shirasawanum, sold as a palmatum cultivar (e.g. 'Trompenburg' etc) confuses the issue because sometimes these have more lobes. As well as being hairier, japonicum is thicker, which stouter new growth. It rarely puts out the same whippy growth as palmatum ssp, and as well the offspring are much less polymorphic; so there are less cultivars. None the less offspring of dissected japonicum are quite likely to be dissected, which has led to cultivars that are very similar to 'Aconitifolium'. It is quite easy to recognize the difference by eye between japonicum and palmatum ssp. There are no recognized subspecies however there are -- as you will see from MOW -- a few variations: vars insulare (widely spread samara, sometimes 'Itaya' is supposed to be this), stenolobum has very hairy samaras, villosum is tementose on the leaf underside.
yes i'll read every book and news letter of The Maple Society,this thread is one imput for my mind for start ,many thanks :-)))
