Plant elms and tie to switch (9)
I believe the answer is:
mistletoe
'plant' is the definition.
The answer is an example.
'elms and tie to switch' is the wordplay.
'and' says to put letters next to each other (I've seen this in other clues).
'switch' indicates an anagram.
'tie'+'to'='tieto'
'elms' put after 'tieto' is 'tietoelms'.
'tietoelms' is an anagram of 'MISTLETOE'.
(Other definitions for mistletoe that I've seen before include "Christmas berry" , "tempting a smack?" , "it may get you a few smackers" , "Kissed-under plant" , "Plant used as Christmas decoration" .)