Trying to catch normal player commands as a mistake is generally a mistake. You wind up working twice as hard for a result which is half as good.
In this case, you have to be careful to catch every verb synonym (if you added more grammar for “examine”, you’d have to remember to fix each of these mistake declarations). You have to be careful about noun synonyms (this will miss “examine the leaf”, and if you happen to mention green leaves in the room description, the player might try “x green leaf”). And you have to be careful about other verbs (what if the player tries “take leaf” or “feel bark”?)
Then there’s the question of whether the player’s command is really up to printable standards. In Glulx, “X LEAF” will produce the output “You see nothing special about the LEAF,” because the command buffer retains the player’s capitalization. If you include a ten-letter synonym, you may wind up repeating the player’s truncation or misspelling beyond the ninth letter.)
If you really want to be pedantic, complain about the failure to set “it”…
Making two or three individual backdrops is, it winds up, the easy and good solution. (One for “leaves”, one for “branches”.) Or you can make one backdrop with a nice general message about “greenery”.