I posted about this new addition to my garden a few years ago and added it to the photos section of Acer Palmatum species http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=29022 (please note that the link has now changed to http://www.fujiyamagarden.com/page17h1.html) I have just noticed that Gomero now refers to the plant as an Acer shirasawanum 'Hemelrijk' You will note the likeness to 'Trompenbourg' and I certainly bought the plant as a palmatum. For the life of me I can see no resemblance whatsoever to a shirasawanum in the leaf shape etc and would be interested to hear a few views on the subject from those more knowledgeable than myself
I don't know this cultivar personally, but I have a few thoughts, for what they are worth. It is listed as shirasawanum in the 4th edition of Vertrees/Gregory. My guess would be it is a hybrid between palmatum and shirasawanum, which is also what 'Trompenburg' is generally regarded as these days. 'Yasemin' is another suspected hybrid between the two species, and I have noted that several recent introductions described as shirasawanum look as if they may also have palmatum heritage. Does your 'Hemelrijk' flower Sam? A good indicator of shirasawanum parentage is if the seeds are held above the leaves with the samaras pointed towards the sky. As to whether these hybrids, if that is what they are proved to be, should be listed as shirasawanum, palmatum, or simply Acer 'Cultivar Name' is another debate entirely.
I fully agree with Maf, both, Hemelrijk and Trompenburg, are likely hybrids between shirasawanum and palmatums, as are probably many others sold as shirasawanum (Gloria, Yasemin,...) or palmatums. For Trompenburg it is certain since the seed apparently was collected from a palmatum but the flowers and samaras are clearly shirasawanum. For Hemelrijk it is suspected, although one cannot exclude unique shirasawanum progeny since seeds were collected from a shirasawanum and flowers and samaras are also shirasawanum-like. To be fully compliant with accepted nomenclature rules they should, as Maf points out, be named Acer x New Name for those hybrids 'Cultivar name'. However, since the people who selected them chose not to do it, it seems quite complicated to operate such a change. Maybe it could be task for the 'Maple Society? ;-)) Gomero
Trompenburg has always been recognised as a palmatum so far as I am aware. Hemelrijk was sold to me as a palmatum (not that that matters much :)) I can certainly see Trompenburg as being in the parentage of Hemelrijk. I see that Gomero knows that the seed for Hemelrijk was collected from a shirasawanum and that flowers and samaras are shirasawanum like. I didn't know that I have yet to see flowers or samaras on either of these two trees in my own collection, but I will be keeping a keen eye ......
