what are the roots of a cypress tree called?

Answer 1

If you mean the portions of the Bald Cypress that stick up out of the water, those are called 'knees'. I think it is a poetic way of picturing the tree as an old man, seated on or near the banks of the swamp.
The correct terminology for these is 'pneumatophores', but I think 'knees' is better; everyone understands what you mean when you say 'knees'.
Some other trees also have these protrusions and there are other names for them.

See this article for more:

http://waynesword.palomar.edu/ecoph30.htm

Answer 2

cypress roots

Answer 3

If you are talking about the part that sticks up into the air, it is called a "knee".