I can't suggest anything specific but I think a number of the same plant set out in a sinuous S curve starting behind the tree and coming forward would look good. Maybe white Cyclamen hederifolium with variegated or silver foliage? Or a yellow grass or sedge?

Thanks @floraluk2 for the suggestions. (We have a good experience with Carex Ice Dance sedge in another location...so for sure an option to consider.)

I would strongly advise against annuals or any other plants that require routine cultivation or digging and dividing. Japanese maple roots are very shallow and resent any disturbance and disturbance or damage in the root zone opens pathways for disease pathogens - like Verticillium wilt - to enter, infect and ultimately, kill the tree. This is a common issue with highly susceptible species like JM's.

Instead, look at some sort of low growing, spreading groundcover type plant. Floral's suggestions are good but there are many others. Something that will spread to fill the area without any need for frequent division or requiring routine replacement/cultivation.

How about one of the types of wild ginger as a groundcover?

I agree with floral, the Cyclamen Hederifolium would be lovely in that area. I think the pop of white in that area would add interest amongst all the green. A Toarella

Whoops, that post didn’t go right!! A Tiarella with white flowers could work too.

debra

A Tiarella with white flowers

debra, I love Tiarella but I have difficulty keeping it more than 2...maybe 3 seasons. For me it just slowly but surely fades away :(.

ditto here re tiarella... :-(

But for sure so very pretty in the spring.

I like gardengal's suggestion of a low groundcover. Something very low will set off the other plants, particularly if the texture is fine and the plant is evergreen

I agree "D M". A groundcover could nicely fill up the bare space.

I can see some ‘all gold’ Jap grass there…it would brighten it up : )

I hve trouble with tiarella too. My only suggestion is to add a lighter color…..light green or yellow. Autumn Bride heuchera will grow anywhere. I will try to add a photo.

Autumn Bride growing at the base of 40yo maple. They get lighter in more sun exposure.

Sherry

You cannot legitimately make comparisons of the roots of Japanese or other Asian maples with that of our large growing native species. They are completely different. Asian maples do not display any root "dominance" - in fact, they coexist with other shallow rooted plants (shrubs, perennials, groundcovers) with ease. They do not smother smaller plants nor do they hog soil moisture or nutrients. Having grown dozens of them personally and sold and planted scores more for clients, I can say that with very high degree of assurance. But they do have very sensitive root systems that are easily damaged, unlike their giant north American cousins. And they are far more prone to Verticillium wilt than the NA species and the main cause of VW infection is root disturbance/damage.

If you don't care about killing your JM, do whatever you like. But of you value your JM - generally much more expensive and valuable trees than sugar, red, or silver maples - then avoid messing about with the roots!

They do not smother smaller plants nor do they hog soil moisture or nutrients

You beat me to the punch 'gg'.

As a side note these impatiens were under our JM (acer aureum shirasawanum) from last summer.

(But 'gg', I will take you advice and stay away from a yearly planting of annuals to minimize disturbance of roots.)

We're not recommending grass. We're talking about suitable shallow rooted perennials which will tolerate deciduous shade and dry soil. Cyclamen hederifolium thrives in those conditions and grows happily among tree roots.

You can grow plants under trees. You just have to choose the right plants. The white trunk belongs to a nearly forty year old weeping silver birch.

The large tree in the background is a Japanese Maple.

they do not have an aggressive root system, are not water hogs and coexist with other, smaller plants just fine.

As one who has several JM, this echoes my experience.

I like the idea of a gold/yellow Carex or Haknechloa. A mini Hosta such as Lemon Lime could work very well too. It is very bright then after flowering it turns more chartreuse. It is very fast growing and divides into segments without cutting when dividing.

Definitely 'peren'. I have had a very good experience with a yellow Japanese Forest Grass.

epimediums...so many, so lovely. I grow 'Pink Elf' and geranium nodosum 'Silverwood (not an aggressive seeder) under my ceanothus.

Several of us responded to a post from robert which has now been deleted. So if some answers look like non sequiturs that's the reason.