Tough question. Depending on the sources, Acer buddiensis, aka Acer buddies, is also mentioned as Acer palensis, the latter being a bit outdated, and I confess I have a preference for it, though I've never addressed anyone with "hey buddy", or "hey, pal", mec... <LOL>
"Natural" companions : these self-sow in the jungle. Campanula persicifolia. Most of them are blue, but the first one to show is white : I have another species, I got it from my late father who died 30 years ago, and each year, some bloom : My pinguicula 'Tina' is a companion for my bonsai. You can see that it's going to bloom, she's had a banquet of gnats, huh huh...
Blue Campanula : PS : I don't know why, or what it shows, but I often associate things with music, or songs. "Une campanule" is also the term for a small bell, the kind attached to the neck of goats or mules. There's atraditional song that begins "Petites campanules qui tintez au cou des mules..." You can guess what "cou" became in our version when we were kids. <LOL>
There's one species of wild orchids that come back every year, a good excuse for not mowing this part of the garden, Orchis bouc. And there's also one or two Ophrys apifera that flower now and then : They're actually companions to the local maples species that can grow in a calcareous soil...
Mentha corsica has definitely settled in. As the name indicates, it's from Corsica, and around the Mediterranean sea. I now find it in many of my pots. The flowers and probably the seeds are so tiny that I think it's because of the wind. It likes a warm, mostly shaded place ; it's used in cuisine in Corsica from what I've read. No wonder, just a small amount is very fragrant. It's become an ubiquitous companion for most of my trees. And a very nice "kusamono" for bonsai. The roots are not invading like much larger mints, they seem to reproduce mainly from seeds. If anyone's interested, I can send you some in late spring/early summer.
Wow, that's really nice. Maybe you can send me some next time we send? :) (I did triage on pentaphyllums, all the larger ones now come from you. About a 50% loss rate on the first year seedlings though. Will post elsewhere.) Glad you revived the thread as I've been meaning to post Feverfew. It's a marvelously good "cottage garden" plant, seeds everywhere and makes lovely little white flowers. A lot like chamomile, but don't make tea with it. If you have to eat it -- for migraines -- the best way is supposed to be with bread and butter. It does taste nasty.
I am of the opinion that JM's in containers grow best with companion plants growing in the same pot. Obviously you have to weed out the vigorous weeds but small species seem to be able to co-exist well. Lots of violets in many of my pots. Also looking at planting more early spring bulbs in the containers, they do most of their growing before the maples leaf out so no competition at all and would help to use up any excess moisture in early spring.
Callistemon - bottlebrush I’ll get a better photo when my other ones flower, this one took a battering with wind and torrential rain soon as it popped