Most cannabis plants that has normal genetics can be grown into trees
...as said a good example is mothers but i guess there is a point when it get too big or too old.
from what i've read ppl tend to keep a mother for max 3 years or so and then just cloning it into a new permanent mother. plants that old looks pretty interesting, they dont have a green stem anymore and start looking more like a small tree
no idea if they even have something that could be similar to bark.
Allso seen a grower doing some alternative methods like regrowing the same plants over and over again.
He harvested them and then recycle the plants by going back to 18/6 or 24 hours of light and then they start veging again still being all females without stressing them going all hermies. He said that he had been using the same plants for about 2 years, haven't seen many doing it tho.