I'm fairly new to the landscaping world and even newer to the JM club. Actually until last year, I thought all JM's were red. I got my first (Peaches & Cream) in September, and am up to 14 and counting (only two of which are red). But now, I pay a little more attention to what people have planted in my daily travels. There is one in particular that has caught my attention. It seems to be half red and half green. You can't see very well from my pics but it seems to have a single trunk. How can this happen?
I do so love that Chimera is the first to respond... The graft is what I thought, too, or do ornamental maples get grafted onto different rootstock? Sometimes a sport. or a reversion, or a variegation will occur at seemingly random times. I've seen all white flowering crepe myrtles have one branch bloom in lavender. I don't know if an actual chimera could occur in plants. Something else to support the graft theory is that the habit of growth is different, too.
The understock is back-budding because the Scion (or red variety that is grafted onto the green understock) is severely stressed. The understock is trying to survive as the red variety is on the decline and may even die. I have seen some intentionally mixed grafting on some lace leaf varieties where they use red and green varieties on one tree. It looks a bit odd to me and they never really caught on.
From the pictures look like there are some shoots from the rootstock not scion but the owner didn't care to prune them or perhaps intentionally left them on. I have one red dissectum Inaba Shidare on high T graft and the rootstock shot a branch of green linearilobum by accident thus in the falls this tree shows two distinct color quite nicely.
There is some evidence of DNA transfer across the graft, so many producers graft red on red. But not all. In fact the whole understock business in maples, Japanese or others, is a nightmare. Greenhouse produced understock is frequently not hardy, or is sick, and is possibly the main cause of maple losses for the gardening public. Further not much attention is paid by most grafters to the vigor of the stock, so that a maple meant to get big, grafted onto dwarfing stock (by chance) will never grow much or only slowly. Or the other way around. As JT1 pointed out the top part is unwell which is encouraging the understock to bud and grow. I guess it is probably too late to save the red part of the maple and it will eventually die. -E