The most common and most likely answer to this crossword clue is the 4 letter word IXIA
I've seen this crossword clue in The Guardian
I
X
I
A
More clues leading to the result IXIA
Buddy explains!

The straight part
We know that "plant from South Africa" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plant from south africa = ixia.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 IXIA mean?
IXIA noun- Any of the genus Ixia of cormous plants native to South Africa.