NEW JM cultivars come from chance crosses that result in unusual characteristics, deliberate crosses that attempt to combine the characteristics of two existing plants, or from mutations on existing plants called "sports" or "witches brooms".

If you found an unusual variety you certainly could graft it and name it. However, very very VERY few plants are unique enough to warrant being named. It takes a very long time to bring an new variety to market - ususally 10 years or so just for testing and observation. Then many more years to grow enough grafted trees to put on the market.

It may seem like there are a lot of varieties, but if you stop to think how many millions upon millions of seeds must be produced to find just one unusual plant, you begin to see why ony a few new varieties appear each year.

Regards,

K4

K4,
That brings up another question. How do you "cross"? And what is a deliberate vs accidental cross. BTW I'm not trying to invent something new here, just very curious about how all this works. You don't see nearly so many variations with the large North American maples (sugar, red, etc). Just wondering why the JMs are so plentiful with different cultivars. And one more question. Did JMs originate from a large "ordinary" maple that was cultivated into a JM or did they just exist this way from the beginning?
Thanks

The genus Acer is pretty diverse, comprising some 124 species indigenous to most parts of the northern hemisphere. Where the species originated has a lot to do with their growth habit and appearance. Outside of North America, Asia is arguably the center of the largest variety of species and with the greatest amount of diversification, with China and the Himalayan countries leading the way and Japan not far behind.

Japanese maples, Acer palmatum, have been cultivated in their native country for hundred of years and do account for the largest number of cultivars (over 1000 registered). Assumably, all orginated from the straight species A. palmatum, however there is considerable diversification even with the species and there are various subspecies, varietals and forms.

Why A. palmatum has such diversification of forms, colors and habits - more so than any other species - is unknown. Vertrees concludes "this species has a strong genetic tendency to proliferate into many variations, mutations and sports." This genetic tendency together with centuries of careful breeding and selection are why there is such a huge variety of Japanese maples. Most of the distinctions between the different cultivars we see today are the result of sports and bud mutations rather than seedings, although no doubt that also accounts for many of the selections. Chance seedings - or accidental crosses - are those that occur naturally, without any intervention from man. Deliberate crosses are made by breeders, taking the pollen from a parent plant and fertilizing the flowers of the second parent plant. Obviously with larger trees that produce multiple flowers, this is a process that is much harder to control and likely accounts for very few new cultivars.

Check out Vertrees Japanese Maples at your library or book store for a more indepth study of this species. This is considered to be the authoritative text on JM's.

I think gardengal did a beautiful job covering this topic! Fantastic! However, I do think there are more deliberate crosses being made now days than one might think. Growers are catching on to the growing collector trade, and plant patents now give growers the right to collect royalties on plants they develop.

Also, I think I need to make a small correction. Not all of the varieties originated with Acer palmatum. One of the reasons there are so many Japanese hybrids has to do with the greater number of species that can cross with each other in Japan, as opposed to North American varieties. Here in the US, we generally think of Sugar Maple and Red Maple when we think of maple trees. These species do not hybridize with each other. However, in Japan there are a number of species that can hybridize with each other. These include Acer palmatum, Acer shirasawanum, Acer japonicum, Acer palmatum dissectum, Acer amoenum, Acer matsumarae and Acer linearilobum (considered sub-species), and also maples from China and Korea - Acer sieboldianum and Acer pseudosieboldianum. Now, think what happens when someone brings these many species together in close proximity to each other in a garden setting. Naturally there will be many more hybrids produced than one would normally see in the wild. So the fact that the Japanese have brought these plants into their gardens for hundreds and hundreds of years helps explain why so many varieties developed. This, plus the Japanese have a knack for hybridizing things (look at KOI!) and also are extremely observant. The result - a thousand varieties and counting!

K4

K4, I'm not sure the literature supports your premise :-) Hybrid maples are not all that common, either here in North America or in Asia. The genus just doesn't lend itself to ready or easy hybridization.

And this may be treading into taxonomic technicalities but a hybrid is a cross between two genetically distinct species. What are often listed as separate species - amoenum, matsumarae, dissectum, linearlobum, etc. - are all either subspecies or varietal forms of the same parent species, Acer palmatum, with similar genetic makeup. So any crosses that arise from these are not accurately considered hybrids but only cultivated forms (cultivars). And to be honest, the term 'hybrid' tends to get used very loosely by those outside of the propagation and plant breeding world, when in fact they should be using the term 'cultivar'. That also leads to a lot of confusion.

The 1000 (give or take) registered cultivars are just that - cultivars, not hybrids.

I can think of only a couple of true hybrids of A. palmatum and other species (A. circinatum for one and A. shirasawanum for a couple of others) and depending on the source, even these are somewhat suspect and still open to DNA verification.

OK, thanks for making that distinction Gardengal. I think perhaps we should be using the term "varietal crosses" instead of "hybrids" to describe the new trees we're seeing then? Varietal crosses would be more common; hybrids rather rare.

K4

'Varietal crosses' is good, but doesn't really take into consideration all those selections that have come be through sporting or other genetic abnormalities on existing trees, which account for a lot. And since all of these are considered cultivated varieties of the same species, Acer palmatum, regardless of how they came to be propagated, 'cultivar' is the correct term to use.

I believe that currently there are far more than one thousand JM cultivars in the trade. Getting back to kj's question the selection process isn't consistent or rigorous. Plenty of new cultivars are completely bogus. And probably 85% of all new cultivars have been named in the last 35 years. Consumerism certainly accounts for a big part of the explosion in spurious cultivars.

Also contrary to what is widely believed in USA maple circles Japanese gardeners are not at all maniacal about introducing, collecting or growing the cultivars.