Acer shirasawanum, or the "Japanese Full Moon Maple," is a species in the section Palmata, named after the Japanese botanist Homi Shirasawa. It was introduced into Europe in the 1800's, coming from the islands of Honshu and Shikoku in Japan. It will readily cross with Acer palmatum, as a number of cultivars exist, and I suspect it would also hybridize with other species, such as Acer circinatum and Acer sieboldianum, to which it is similar in leaf size and shape, but I do not currently know of any examples.
Acer shirasawanum forms a small broad-canopy tree. Leaves are normally green and round with nine to eleven lobes. For me, the feature that distinguishes this species from Acer palmatum is that the seeds rise above the foliage. Some hybrids of Acer shirasawanum (with palmatum), such as 'Red Dawn' are clearly not full shirasawanum, as frequently listed. Perhaps one parent is truly shirasawanum, but I have a difficult time including them in that group...if the seeds hang down. And, it has been said that 'Red Dawn' is my cultivar, but it is certainly not. I have no idea who introduced it--please come forward!
The gardening public couldn't care less if shirasawanum and palmatum get confused, but perhaps they should. Shirasawanum is generally considered more winter-hardy of the two, so in marginal hardiness areas the shirasawanum would be a plus. My many years of growing experience has shown me that shirasawanum cultivars have survived tough winter freezes, where the same age and pot size of palmatums have perished, even though both groups share palmatum as rootstock.
Recently a maple novice--who fancies himself as an expert--said that the palmatum species is the best of all the maples because of its variety, because every leaf shape and color is possible. Well, there's certainly more cultivars of palmatum than with any other species, so I would have to agree with his statement. But my natural inclination is to argue and to find exceptions to any theory or rule, so today we'll celebrate the shirasawanum species for all of its diversity.
First, I'll brag about my own introductions. We have green laceleafs, red laceleafs, green uprights and red uprights. All originated as seedlings from shirasawanum mother trees, all in an open garden setting. Therefore they could all be hybrids, or none of them, but in every case the seed rises above the foliage.
Acer shirasawanum 'Kawaii'
One of the most exciting of any maple introduction is 'Kawaii', which means “cute” in Japanese. This plum-red finely-dissected laceleaf was named by my wife, Haruko, when she first saw it. She didn't intend to name it, rather it's what she said when she saw it. 'Kawaii' is a slow-growing spreader to one foot tall by three feet wide in ten years. It doesn't really “weep” like many of the red palmatum laceleafs, although occasionally long shoots will develop and arch downwards. It must receive a good deal of sun for best color; plants grown in shade tend to be greenish.
Acer shirasawanum 'Green Snowflake'
|Acer shirasawanum 'Delicut'|
I've seen a lot, but I haven't “seen it all.” But if there exists another red laceleaf shirasawanum cultivar, I don't know about it. Anyone? Similarly, with a green shirasawanum laceleaf. Our 'Green Snowflake' displays small, dissected pale-green leaves. It too is a spreader, but much more vigorous than 'Kawaii'. Another green laceleaf is 'Delicut', which has more refined foliage, and is probably a hybrid with palmatum. Both of these laceleaf cultivars display blazing yellow to orange autumn color.
Acer shirasawanum 'Mr. Sun'
|Acer shirasawanum 'JB-F'|
|Acer shirasawanum 'Claire'|
'Mr. Sun' is a stocky green upright with leaves shaped like a child's version of the sun. Long lobes roll downward and taper into sharp points. It is similar to 'Claire', but that cultivar hasn't made it into our production, and probably never will. 'Green Flag' was in production years ago, but has since been discontinued due to weak sales. Same with 'JB-F' which never even got out of the code-name stage.
|Acer shirasawanum 'Shira Red'|
All of the discontinued selections are nevertheless nice trees with pretty foliage. “But enough, Buchholz!--you can't name every damn seedling you raise,” I can imagine many of you saying. Well hold on because I'm not finished yet. When I bashed 'Red Dawn' earlier, all based on drooping seed, I must say that I have the real deal: a cultivar called 'Shira Red'. It has the same color and leaf-shape as 'Red Dawn', and also the same vigor...and the seed is erect.
Acer shirasawanum 'Sensu'
|Acer shirasawanum 'Sensu'|
|Acer shirasawanum 'Sonya Marie'|
Acer shirasawanum 'Grace'
My favorite shirasawanum introduction for fall color is 'Sensu'. It is pretty in spring too, with fresh green foliage. My wife and I were admiring the original seedling one evening, and enjoying the pleasant spring breeze. 'Sensu' became animated, like it was trying to tell us something. Haruko was delighted, and described it as a geisha waving her fan. Sensu is the Japanese name for “moving fan.” Autumn color varies from year to year, but the photo above shows it at its best. 'Grace' is similar, except for more red in its spring foliage. 'Sonya Marie' was initially promising, with cream-white variegation splashed amongst the foliage; however, as the trees mature, the variegated leaves become difficult to find.
Acer shirasawanum 'Johin'
|Acer shirasawanum 'Johin'|
Acer shirasawanum 'Haru iro'
What maple collection could do without 'Johin'? Haruko thought it was “very elegant” when she first saw it, hence the name. Maple collectors and producers get kind of tired of the purple-red selections, such as Acer palmatums 'Bloodgood' and 'Tamuke yama'. Once we develop a thorough case of “maple fever,” we start appreciating the plum-reds or brown-reds. And 'Johin' is especially nice in spring with its prominent lime-green veins. 'Haru iro', or “spring color” in Japanese, is similar to 'Johin', although with more green at the leaf base. Far more choice of the two is 'Johin' I think.
|Acer ? 'Little Fella'|
'Little Fella' originated as a dwarf seedling from 'Johin'. It too displays plum-red foliage, but the leaf shape and rate of growth set it apart from 'Johin'. It hasn't produced seed yet, so I don't know what species it is until then, even though the mother is a shirasawanum.
|Acer shirasawanum 'Green Flag'|
|Acer palmatum (or ?) 'Green River'|
Hey, am I making up botanical rules as I go along? What are the rules anyway? I've discussed these nomenclatural issues with some well-schooled “experts” who can't give me clear answers. One remarked that it would make a great dissertation for a graduate student. Maybe I've missed something along the way, and there already are set rules to determining species. For me, I can't use an “x” to denote a hybrid, because I can't be sure if my selections really are hybrids. And consider this dilemma: shirasawanum 'Green Flag' produces erect seed, while palmatum 'Green River' displays pendant seed, but they both share the same parent, shirasawanum 'Palmatifolium', and were germinated the same year. Of course 'Palmatifolium' could be a hybrid. Please Flora, you're messin' with our heads!
This web log has worn me out, just with my own introductions and theories, so I'll end it with just photos of other worthy cultivars. Hopefully you will have developed a stronger appreciation of the diversity within the shirasawanum species.
Acer shirasawanum 'Aureum'
Acer shirasawanum 'Mirte'
Acer shirasawanum 'Jordan'
Acer shirasawanum 'Moonrise'
|Acer shirasawanum 'Microphyllum'|
|Acer shirasawanum 'Microphyllum'|
|Acer shirasawanum 'Autumn Moon'|
|Acer shirasawanum 'Ogura yama'|
|Acer shirasawanum 'Gloria'|
|Acer shirasawanum seedling selection|