The most common and most likely answer to this crossword clue is the 5 letter word PHYLA
P
H
Y
L
A
Buddy explains!

The straight part
We know that "Parts of kingdoms" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case parts of kingdoms = phyla.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PHYLA mean?
PHYLA noun- A tribe.
- A rank in the classification of organisms, below kingdom and above class; also called a division, especially in describing plants; a taxon at that rank
- A large division of possibly related languages, or a major language family which is not subordinate to another.