Got this at a greenhouse about 10-11 years ago - neglected in a corner all by itself.
I'm almost positive that it's one of the Brachychitons (I had it narrowed down and wrote it down somewhere at home but haven't searched for it lately) but note that mine still has 'juvenile' leaves.
I'm wondering if anyone has any ideas on how to remove or minimize the salt/lime (whichever it is) buildup on the caudex?
It's a very 'woody' caudex with many 'fissures'...not sure if I can remove this buildup or not.
I am only getting my info from an Asian couple who grow these in Aransas Pass, Texas...big Asian population on the coast in Texas...she says if you grow from seed, you will only get about 4" of growth a year with adeniums, but the caudex gets real big and the plant has strong big stems and branches out beautifully. If you grow by cuttings, you won't get a bix caudex and the plant stem stays relatively small with little branching...she told me this today when I saw her.
Looks like B.acerfolium Nan. Funny story to follow(ha)...Mine looked the same as yours,and i was going to grow it as a bonsai...after a couple of years decided to plant it in the ground. Well,years later it's 12 feet tall with a reed thin trunk and the same tiny juvenile leaves-just a lacy amount more.Stunted,yet,not really dwarfed. That's a new one to me. How large they can get and stay in the juvenile mode i don't know. At least the new leaves are a vibrant red,before turning green.
You might try a toothbrush and baking soda to gently scrub the salt minerals off the caudex. Make sure to wash off the soda.
Looks like a B. rupestris to me. I have several of the B. acerfolium and they never looked like this even as seedlings.
I don't know about Wisconsin, but the B. rupestris is harder to find than the acerfolium.