I don't need cold to grow well - Odd tree observations

Just something I noted sometime ago.

The so-called Indoor Bonsai exported from China come to mind.
For example -

[1] Serissa
[2] Chinese Elm
[3] Privet
[4] Sageretia
[5] Fukien tea

All come from areas with some cold, and it has been proven the Serissa can handle the zone 7 cold of New Jersey.
Would be interesting if someone could also test all of the above for zone 7 [ perhaps I can ask Carl R.]

Sub- tropical

[1] Celtis [ Chinese ] the other types Africana, Europa, American types seem to need refrigeration / cold
[2] Olive
[3] Pomegranate n.
[4] Swamp cypress

Now here is the kicker - Olea a. needs no cold to live on, nor does the Podocarpus or the Japanese black Pine.
In fact there are many trees from China that need no cold to continue growing and grow well such as Murraya or Citrus.

Do these and many other trees carry a " Tropical Gene" from the ancient days of a totally Tropical earth ?

How many trees are there, that can be used successfully for Tropical Bonsai coming from cold / warm seasonal areas worldwide ?
Just wondering.
Khaimraj

* Looking at trees or shrubs, that can back bud easily on old wood and are prone to branchlets.

All these do well in Zone 8... No noticeable difference in health of the trees between "cold" and "mild winters...