Final answer:
The lengthy sentence in question is a simple sentence because it has one independent clause and no subordinate clauses, expressing a complete thought.
Step-by-step explanation:
The sentence "Moss often hangs from the branches of the bald cypress, a tree that grows in swamps in the south." is a simple sentence. Despite its length and the additional information provided, it contains only one independent clause and no subordinate clauses.
A simple sentence can be long if it still contains only a single clause, even though it may have additional descriptive information or phrases. The key is that there is only one subject and one predicate that express a complete thought and can stand alone as a sentence.