In article ,
Tex John wrote:

It is a tree so is herbaceous by definition. Perennial...comes back at least
^
NOT
once each year. Deciduous....drops its leaves. But what is it really?

Correction added :-)

Also, things like angelica are usually classed as perennials, because
they often take 3 years to reach the flowering stage (when they die).
I find that misleading, but it is unclear how to distinguish that
from other perennials that may take 50 years to flower and die (like
some bamboos). The technical term for such plants is monocarpic.

I don't know of any terms for plants that estivate rather than hibernate
(and both of those terms are rarely used for plants), but deciduous
plants and facultative evergreen ones can be very variable on what
triggers them to drop leaves. Any or all of the following can do it:

Cold, as in frost or just continual lowish temperatures
Low light levels or short days
Heat, especially coupled with low humidity
Drought or other physiological stress (including waterlogging!)
Severe aphid, mite and other infestation
General leaf rot, due to cold and wet (common in the UK)

This is why many plants will go dormant in summer or winter in one
place but not in another, or do it one year and not another.


Regards,
Nick Maclaren.