I thought since there doesn't seem to be any personal experience here on this, I would offer the list I've compiled so far:
Attaryi _ x 20'
Emmit's Pumpkin _ x 20' (Info differs on this. Anywhere from 2-4' wide x 6-9' tall, or just plain 20', so TBD)
'Iijima Sunago' 15 x 15-20'
Nuresagi 10-12' x 18-20
Oshi Beni 14-16' x 18-20'
Sango Kaku 18-22' x 20-25'
Tana _ x 12-18'
Tsukasa _ x 20'
Vitifolium 10-15' x 15-20' Maybe 30'

I'm looking at information and experience that would be similar to my climate, which is S. Maryland in very hot sun.

This post was edited by CEFreeman on Sun, Sep 14, 14 at 9:52

Got some more:
'Arakawa' 12-15'
Ariake nomura 15-20'
Asahi zuru 12-18'
Beni Otake 12-16'
Boskoop Glory 8-10 x 12-15'
Crimson Prince 22-25'
Emperor I _ x 16'
Moonfire _ x 12-15'
Omato _ x 18-20'
Suminagashi 15-14 x 15-20'
The Bishop _ x 14-18'
Tsuke Bane _ x 15-20'
Utsu Semi _ x 14-18'
Whitney Red _ x 12-18'
'Yama kagi' _ x 25'

What I'm doing is looking at about 13 different site s & their locations. I'm averaging the heights, since I'm figuring conditions dictate so much.

I have sooooo many short ones that will not provide shade for the dwarfs, I'm really trying to pick up only taller ones now.

Just ordered an Emmit's Pumpkin and will order a Tsukasa! Shade it is! :)

This post was edited by CEFreeman on Sun, Sep 14, 14 at 8:25

Where did you see the 20 ft height for the Emmit's Pumpkin. I'm more of a dwarf tree collector and have that japonicum on my short list as a dwarf. I guess a lot of JM will eventually get to that size but I'm thinking a lot of them on your list will take some time.
The Emmit I believe would grow more like a semi dwarf---- average about 8" a year under normal conditions. If my math is right that would take about 30 years to achieve the size you want. Also your true dwarfs are growing about half that rate but still growing.
My point is that you should be looking for vigorous growing trees not the tallest. You have done the research and probably can answer better than myself. Is your above list compiled by rate of growth or just mature height of tree. I would think rate of growth would be what you are looking for here.

The Emmit just called my attention to this thread. Its a beautiful tree that i thought was a slow grower. I see after a fast google search that it may grow intermediate. Different sites may have listed it as dwarf.
Anyway it looks like you put a lot of research into this subject and I was just looking for clarification on the subject.

First question:
I saw the height listed here:
Mapletopia and
GardenWorldOnline and
Dancing Oaks Nursery.
Many of the other nurseries list it as anywhere from 6' to 9' tall, 2' - 4' wide. I'm never sure. For example, Davidsans has so many typos, that I like reading what he has to say, but as far as specs? no. I haven't located who hybridized the Emmett's (aka Emmitt's or Emmit's) Pumpkin or I'd go to the source.

Second question:
Yes, my next research would be fastest growing. I thought I'd try to narrow the field with the tallest first, then go from there. These specs are more difficult to find. I often wondered if the nurseries are just vomiting what's written on the tags, or if the difference in specs is because they have experience with a particular variety. Growers vs. nurseries are more difficult to differentiate.

We'll edit Emmett as a TBD.

Gardengal48, do nurseries here sell the straight species? All seed grown Japanese maples aren't considered original species are they, just because they don't have a name? My seed grown Japanese maples have a lot of variability. I wouldn't think that would be the case in Japan where they're native.
Here's one of my seed grown Japanese maples growing by the driveway. It's well over 20 ft. tall and over thirty years old. The Dawn Redwood in the background is approximately 80 ft. tall.
Mike

Hey Mike - yeah, technically any seed grown JM is considered just a species Acer palmatum. Obviously, depending on parentage, there can be a huge variability in habit (among other characteristics) so maybe I should qualify my response a bit :-)) Let's just say in general the straight species Acer palmatum has the potential to be a large tree. According to Vertrees, selections from A. p. ssp. palmatum (aka the Palmatum Group) can reach as large as 15m. That's almost 50 feet!

You don't find many species JM's in retail nurseries simply because most folks want named cultivars with specific attributes. But I know a few commercial growers that always have a selection hanging around. As do you :-))

Some accurately measured heights from Jacobson, Trees of Seattle - Second Edition (2006):

A. palmatum

41'
40 1/2'
38'
37 1/2'
31 1/2'
37'
31'

Redleaf or purpleleaf cultivars

37'
'Bloodgood' 33 1/2'
'Bloodgood' 29'

'Butterfly'

22'

Green cutleaf, threadleaf, spiderleaf, laceleaf cultivars

6'

Purplish cutleaf, threadleaf, spiderleaf, laceleaf cultivars

12'
'Ever Red' 9'
12 1/2'
11'

'Shishigashira'

18 1/2'
15 1/2'
12'

Seattle is in USDA 8. I would also recommend looking at the size records for Japanese maples in Van Pelt, Champion Trees of Washington State (1996, University of Washington). One of the sets of dimensions for multiple specimens you will find there are the one for what was understood to be the original 'Whitney Red' at Whitney Gardens (also in USDA 8). You would probably also be interested in seeing what records are given by Jacobson in North American Landscape Trees (1996, Ten Speed, Berkeley) as these are from all over.

This post was edited by bboy on Tue, Sep 30, 14 at 21:19