So I decided not to protect my plants this winter, to see which ones would survive. Well, they all did, and they're all still green as well, except for my pearly gates, which die anyway each year. We had one freeze and multiple frosts, lowest temp was ~ 28 - 30 F. These are the plants which can take such conditions:

Toe - my toe plant is still fully green and actively growing again with about 12 flowers right now.

Chirac Sanango - I feel this plant can take much, much colder temps.

Mimosa Hostilis - lost its leaves but is beginning to lead out again.

Acacia Carrolea - seems to not be affected at all (thanks frog pajamas)

Acacia madenii - same

HBWR - still has green leaves from last year.

Oluliuqui - still green, and even kept growing between cold snaps. This plant is tough, after the first frost it developed hard bark on all of its stems.

Caapi - still green but stopped actively growing, it's budding out again though.

Psychotria (could be Alba or viritis) I covered it for the one freeze but it has kept growing slowly all winter.

Acacia confusa - stayed green and kept growing as well.

HA HA!
I am in Zone 8 so all my babies have been in my clawfoot tub under lights. Just now moving them out to harden them now that the frost danger is mostly past. Great work BFP!

I'm in zone 9. And oluliuqui really surprised me, out of all of the plants I grow, it stayed the greenest through the winter, it basically kept all of its leaves, and looked just as it did last fall, then just took off from there again. You should experiment next winter, you'll be amazed.